I thought down was the way to go. Packs down smaller, higher warmth-to-weight ratio, high loft. I thought synthetic is heavier, has damageable fibers if packed too small, and doesn't pack as small.

I'm all confused now after reading things like "New synthetic insulations, escecially Climashield, are the lightweighter's dream" (posted on another thread) and seeing that BMW's entire Cocoon line is synthetic.

The only benefit I'm aware of is that wet down does no good, and synthetic is safer in this regard.

Someone help me out here!

Advertising for years comes up claiming that "synthetic is now as good ad Down".

If you saw microscopic pictures of good fluffy down, and similar pictures of synthetic insulation, you would tend to believe that the wonderful structure of down developed by millions of years of evolution isn't easily matched by humans squirting resin through little extrusion nozzles.

However, it is likely to be true that real inexpensive down can be beat on a loft per weight by the very best of the synthetics.

Confused? Thank marketing and their desire to mold your mind to get the dollars out of your wallet.

Ryan, I think you have the down / synthetic pluses and minuses covered (assuming we are talking about high quality down):

Down
+ higher warmth-to-weight ratio
+ lighter
+ compresses well
+ loft has longer lifetime
- expensive
- not good when wet

Synthetics
+ cheaper
+ safer when wet
- lower warmth-to-weight ratio
- heavier
- doesn't compress as much as down
- loft degrades earlier than down

I think BPL's philosophy to go with synthetic vs down has important merits.

First, synthetic is safer than down in wet conditions.

Second, by viewing both your clothing and sleeping bag (quilt) as your sleep system - i.e. supplementing a synthetic quilt with synthetic clothing - you can kind of have your cake an eat it to. You have the safety of synthetic in inclement conditions and a light weight system because your clothing is duel purpose: part of a sleep system and used around camp.

Personally I have a mix of both down and synthetic. I use a down bag and synthetic clothing.

My decision on a down bag was one of loft longevity and weight-to-warmth.

My decision on synthetic clothing was one of cost and a margin of safety in the unlikely event my down bag gets wet.

Edited by pappekak on 09/19/2007 09:43:28 MDT.

Ryan:

The only thing confusing is advertisers' irresponsible claim that today's synthetics have approached down in terms of warmth and compressibility. It's a fiction -- and thus no confusion at all.

Use synthetics when moisture is a significant threat. Otherwise, down is still the more efficient insulation.

Both the comments about the marketing of Synthetics vs. Down and the inherent superiority of down are correct. However, you should spend some time tracking down as much of the ongoing discussion of these two insulation technologies as you can so you can make up your own mind.

If you are likely to be out for an extended period of time in cold conditions where you will not have sufficient time to air out and/or expose a down bag to the sun, then the down bag will accumulate moisture which will degrade its insulative properties. Hence the use of synthetic insulation under these conditions. But if your use a vapor barrier to line the bag, this would not be a problem and you would then be back to using down.

Do you see the problem in a one comment solution to this issue?

Both down and synthetics have their place in the outdoors. It takes a knowledgeable backpacker to know when to use each. Become knowledgeable.

> "New synthetic insulations, escecially Climashield, are the lightweighter's dream" (posted on another thread) and seeing that BMW's entire Cocoon line is synthetic.

>The only benefit I'm aware of is that wet down does no good, and synthetic is safer in this regard.


...I'm the one who posted that. As Roger said, you've pretty much summed it up. The reason why synthetics are a lightweighter's dream is that they allow you to wear/bring as much as *all* of your daytime clothing to bed if you want to/have to. And they allow you to do it every night, even if you're damp after the day. That includes your damp base layers, your soaked socks, and your jacket that has absorbed a bunch of sweat during a rest break. By morning, your body heat will generally have dried your duds and you can carry on. Many people choose synthetic insulation because some or all of that moisture may wind up in your sleeping bag/quilt.

The issue is the condensation point. Your body heat will drive vapor from your skin (and damp clothes) outwards through your layers of insulation. At some point, though, this water vapour will cool down enough to condense, and become liquid water droplets.

If the vapour makes it all the way out through your base layer, jacket, sleeping quilt, and bivy *before* it condenses, life is good. You are drying your sleep system with body heat, and there's no concern.

What commonly happens, however, is that cool and/or damp ambient conditions experienced at night will make that vapour condense *before* it has exited your sleep system. This Condensation Point (aka Dew Point) may be located *inside* of your bivy, or it may even be inside of your sleeping quilt. This is a frequent occurrence, especially in climates like the Pacific Northwest and New England, and especially during the shoulder seasons.

If this condensation happens in or on synthetic insulation, no-harm-no-foul. It may feel clammy, but it will still keep you almost as warm while you wait for morning. If, however, you use down insulation? You are in for a difficult night. Your down will start to gain weight and collapse, and will very quickly become into a sloppy mess. Once it's a wet sloppy mess, it holds *no* heat and you might have to start thinking about getting a fire going. (Hopefully it's not raining or snowing. :)

"Well I am careful to keep all of my clothes and gear dry."

So is almost everyone. But as a lightweight backpacker, you probably have fewer options to help you do this. You probably don't have an extra jacket, or a full change of clothes to wear to bed.

Also, your skin gives off moisture all night long. This is called Insensible Perspiration, and it's a process whereby your skin tries to maintain a certain minimum humidity on its' surface. Your wicking base layers are constantly taking this humidity *away* from your skin, and your skin is constantly perspiring at a low level to replace this lost moisture. If it's cold/damp enough, all of that moisture winds up in your insulation. (More than a pint a night, apparently.) Some Arctic explorers report sleeping bags weighing 60lbs by the end of their trip because insensible perspiration has been freezing in the insulation for weeks or months: it's a real and potentially dangerous phenomenon depending on your circumstances.

Since the dew point is generally not *immediately* next to your skin, some people have success wearing down insulating gear inside of a synthetic bag. That way you have synthetic insulation at the condensation point and down where the moisture is not likely to condense. This same down layer, however, will likely be worn during the day -- not practical on rainy+humid expeditions!

There's also the issue of external moisture. The shelters involved in lightweight backpacking are often more prone to condensation than the big double-walled tents of traditional backpacking. If it's cool and rainy outside, this can lead to sleeping in a home-made fogbank all night. Some users have reported actually watching a down sleeping bag collapse over the course of a night.

Finally, many lightweighters are involved in more remote/extreme trekking. A fall in the river, a leaking platypus, or a down bag that becomes soaked during a day or two of humid/rainy camping is no big deal when you're 10 miles from the car. But imagine being 100 or more miles from civilization, at 2 a.m., possibly solo, with a failed insulation system and a bad case of the shivers. Such a scenario is why many experienced lightweight backpackers opt for synthetic insulation pieces over down ones.

I disagree with the below statement. Please review human physiology of sweating. The princeton article online was wrong too and that is why the CDC (it was on their site too) made them take that part out.

The body DOES NOT sweat to maintain a certain humidity percent on the skin surface. Insensible perspiration is an involuntary diffusion of water molecules through the skin due to normal metabolism and is not controlled or stopped by outside influences including vapor barriers.

Outdoor books that many put faith in have wrong information on this aspect of human physiology. Some of the information has been perpetuated since the 60's or 70's from perspiration medical articles that never proved what those books still state to this day.

================
Brian James said,
This is called Insensible Perspiration, and it's a process whereby your skin tries to maintain a certain minimum humidity on its' surface. Your wicking base layers are constantly taking this humidity *away* from your skin, and your skin is constantly perspiring at a low level to replace this lost moisture.

Edited by jshann on 09/26/2007 04:44:10 MDT.

Matt,
Who's post is wrong?

Umm I don't really have a response. I thought I'd read most of that on BPL.

It seems counterintuitive to me, though, that moisture wouldn't evaporate from my skin.

After all, anything that has free water molecules on it, including skin, is subject to evaporation. How is it that skin is exempt from this law of physics?

Also, how is it that Will Steger's sleeping bags got so heavy on his way to the North Pole? It certainly wasn't raining, and airborne humidity at -40 is quite low. How did his sleeping bag gain 35 pounds, if not from moisture coming off his skin?

Perhaps some manufacturers of VBLs would benefit from this revelation as well; they could immediately stop selling a product that apparently has no benefit.

i dunno matt, ive been writing research papers lately and it has been my experience that in order to have a legitimate argument, whether you are right or wrong, some sources need to be cited more than 'the CDC said so' and maybe contain more of an argument than 'thats all flat wrong'.

Despite all of the science behind perspiring, i find synthetics superior to down for me. My 12 oz 40* XP quilt packs to 3 liters, my 26 oz 20* primaloft quilt packs to about 6 liters, both very small. My 14 oz thermawrap parka packs to about 2L as well. Differences with down are negligible in both weight and size until you get into 4 season. Syn is cheap, easy to make and modify, and I have no reason to carry a bivy (6 oz at least). I do believe that advances in sleep gear design can lead to 20* syn bags that are as light as 21 oz with a small zipper and hood. That compares to pretty much every down bag of similar temps. Synthetics are almost there, but have a little more work to do before they reach total warmth/weight with 800 fill down. The other benefits i believe outweigh the difference already.

Concerning getting stuff wet at night with sweat, i try to stay very close to the limits of my sleep gear because I hate sleeping hot and it just doesn't feel right waking up cozy and warm on the trail. sadly, sometimes i carry too much sleep gear for the temps and I sleep like most people like to- warm. I have a hunch that whenever someone is 'properly' prepared for the weather they encounter, they will sleep warmly. sounds pretty good. i also think that when you are warmer than you need to be, your body perspires to cool you off. i hypothesize that this may be the cause of the wetness in peoples bags at night. The north pole fella may have either been sweating a bit at night because he was warm and prepared, or he wets the bed at night and didn't tell anyone. just my 2 cents

Brian wrote:

> It seems counterintuitive to me, though, that moisture wouldn't evaporate from my skin.
> After all, anything that has free water molecules on it, including skin, is subject to evaporation. How is it that skin is exempt from this law of physics?

Very good question, and the answers are important for us.

There are substances called 'poly-alcohols' which have some quite amazing properties. One is that they can be spread out extremely thin yet remain a continuous film. Another is that they are fairly opaque to water transport. So if you took a cupful of a suitable poly-alcohol and poured it onto a dam, it would spread right across the surface of the dam and block all evaporation. Quite amazing. Of course, a bit of wind and a few ripples and the film would be broken, but never mind.

Left to the forces of the environment, your skin would dry out amazingly quickly and become most unhealthy. A bit like sun-dried meat. It avoids this by generating its own poly-alcohols - aka skin grease, and this thin layer stops surface evaporation from your skin. So cool skin does not evaporate very much at all.

When your body needs to pump out heat for cooling it opens up pores on the surface and these pores allow direct evaporation. This is sweating. Sometimes the amount of moisture being pumped out exceeds the surface evaporation capacity and free moisture results: wet sweat, drips on the face, etc.

The surface evaporation capacity can be exceeded when the air surrounding your skin becomes saturated. Hot still days are good for this. On the other hand, a good breeze will strip the humidity away from the surface of your body, allowing better cooling.

So a cool dry body which has NOT been freshly washed may lose very little moisture while asleep. On the other hand, soap and water will remove this skin grease and let you sweat more easily. But note that lots of salt on the surface of your skin may upset the poly-alcohol layer. For this reason it makes sense to rinse your skin in the evening to remove sweat salts, but don't use any soap or you will remove the valuable protective skin grease layer.

Cheers

Thanks for the info, Roger. The "that's all flat wrong" guy seemed to be suggesting that the humidity next to our skin was not relevant to the amount of moisture lost to a sleep system, and/or that none of the skin's moisture migrates to your sleep system during the night. Or something...actually he didn't really say anything, so I had to infer these statements by inferentially parsing his ambiguous negativity.

I don't doubt that the skin is well adapted to inhibit unwanted moisture loss. Otherwise we'd all (being 96% water or whatever) look like dried apricots and have to drink 10 gallons of water a day. You Aussies would have to just connect your veins directly to the kitchen taps!

Poly-alcohols or no, though, I still believe that everybody (every body) loses water through their skin into their sleep system. Particularly if (as you mentioned) there's some salt on your skin from the day, and particularly if 98% of your skin's poly-alcohol-excreting surface area is being constantly rubbed and scrubbed by a freshly washed piece of polypropylene or wool.

This is why a VBL adds such an amazing amount of warmth to a sleep system, despite being an inherently noninsulative item: it's only function is to stop moisture transport, and stopping moisture transport alone makes a substantial difference in your ability to stay warm.

That's what I was trying to convey with my post.

Brian

The hotter it is the more you sweat. Some people sweat more than others. You always sweat unless you are freezing to death. It is all relative. I would love to be able to take along a lighter weight down bag but... Lugging along a household dryer is out of the question. On many a night I went to bed in my synthetic sleeping bag with damp clothes and the extra damp socks circulating around in the sleeping bag. The next morning PRESTO! Everything dry and I could have filled my water bottle with the condensation on the inside of the tent (MSR Zoid)! If it's windy and I can set up the tent with the foot to the wind that problem disappears too.

I agree that a synthetic bag is a wonderful clothes dryer and I use one for climbing for that purpose. I also agree that a synthetic bag might negate the need for a bag cover/bivy under a tarp or in a condensation filled tent.

However, after using PG Delta, 3D, and Primaloft, I have yet to find a synthetic that keep sme as warm as good down (all things being equal).

For instance, I like my DAS Parka for a belay jacket, but when it is cold (between 10-20) and I am standing around belaying, I have yetto be really warm. In fact, my MH Phantom down jacket keeps me warmer- even with no hood and a waist length cut... I have noticed this with bags as well.

My solution is to use a lightweight down jacket and a synthetic bag in the hopes that the bag will dry any moisture in the jacket during the night. After a weeklong trip in the Cascades last spring (very wet and constant ice or snow), I noticed no loss of loft in my down jacket (Phantom). I slept in it inside a 20 degree TNF Delta PG bag (what is that one called?).

I have an old down jacket but would like to upgrade to a much lighter synthetic option. I like to canoe and kayak, so synthetic seems like a better choice there, plus in a survival situation I would think I would be less likely to wet out a synthetic jacket in snow/rain if I was injured and/or just lost.

But I found this BPL article on the subject to be interesting about the relative drying time of down vs. synthetic:

http://www.backpackinglight.com/cgi-bin/backpackinglight/wet_weather_performance_down_vs_synth_vests.html

"surprise discovery - the down Flash vest recovered loft as quickly as the synthetic Micropuff and after 30 minutes of drying its loft exceeded the Micropuff's."

I will say in my experience of washing and drying a down bag and a polarguard bag, the PG bag is much less wet and clumped after washing, and dries much faster to me.

I interpreted that article to conclude that only extremely thin, lightweight vests resulted in similar drying charateristics. I don't believe that they intended to infer that the same results would apply to thick sleeping bags, using down vs sythetic insulations.

Personally, I use synthetics for clothing that is exposed on the trail to the elements (sweat, rain and wet vegetation) and I use a down sleeping bag since I have the protection of my tent. I also, don't do long distance hikes. Mine are limited to 2-4 days.

Edited by mad777 on 09/19/2007 20:44:13 MDT.

Loft recovery in little vests on active people is a different animal than loft recovery in a 2" thick quilt on a sleeping person.

Once your down is soaked, it will take a *huge* amount of heat energy to convert all that water into vapour and restore the loft of your down. And extra heat energy is something a sleeping person doesn't have. (Hence the need for a sleeping quilt in the first place.)

We seem to have two different threads in one here; unless you consider the overlap of sensible perspiration affecting down more than synthetics.

Anyway, the following acronym I use might help some new members realize the factors involved in insulation choices. Expereienced members already know this.
I choose insulation based on METTT; the
Mission (fast and light, car camping, etc)
Exposure (water, snow, ice, humidity, tarp or enclosed tent, etc.)
Terrain (fuel-less alpine or forest, etc..)
Team members (all carrying down!?), and
Time (long damp durations favor synthetics)

So a week on the Olympic coast results in a different combo than a weekend on a dry mountain top. And if one person is carrying all down you might want to carry a synth as a backup. With UL backpacking your insultation is a system; for example a jacket would be worn when active, and to boost the insulation properties of a lightweight bag.
Personally I favor a synthentic MB Thermawarap set in a light down bag.

Has anyone here been really wet in a synthetic bag? I have and I can tell you that I didn't notice much in the way of thermal properties. While synthetics (and excuse me here cause I ain't much of a scientist) may be a bit more tolerant of wet conditions, in really wet conditions neither one is "safe" to be in. Just pointing out that "safer" is a pretty relative statement in this case and shouldn't give a false confidence in synthetics.

Yes, soaked, but you can ring synthetics out (not too harshly though), which helps their thermal efficiency a lot. It gives a bit of a cushion in a worst case scenario.

I think the susceptibility of down in wet conditions is vastly overstated. Down has some natural water resistence, if you get the surface of your bag/clothing wet it will dry without much trouble. Surface meaning not thru-and-thru wet. Also a good water resisitent shell goes a long way.
The only advantage of synthetics besides cost is the abillity to ring and sqeeze the water out.
If your bag is soaked to the core like that than you had to have done something really, really stupid.

Edited by MAYNARD76 on 09/20/2007 05:48:14 MDT.

I think it's understated.

Last winter I changed my dry body into dry clothes, laid down in my dry down bag in my dry well-ventilated tent, and drifted off remembering that it was humid so I'd have to wake up and check for condensation.

In the middle of the night, a cloud drifted into my tent. I had proper low-high ventilation arranged and I was ready for humidity. But I could actually see the wisps of cloud/fog moving around the tent and drifting in the vents.

If I'd closed the tent up any more, I would have been in a condensation bubble.

By morning, my down bag was like a sack of wet leaves. Whereas it was previously at its' maximum compression in its' stuff sack, it now took up *half* the stuff sack.

I was camping on 15' of snow, and there was wet snow falling. There was no *way* I could have dried it out. I thanked the deities that I was just on a gear-testing overnighter, strapped on my snowshoes, and got the heck out of there.

As stated, if it had been synthetic I would have at least had a fighting chance. But if your METTT involves humidity that hovers just above or just below freezing, you could reach the failure point of your down despite doing everything right.

Synthetic just has a more extreme failure point in terms of humidity/moisture saturation. Also, it's possible to bring it back from the dead using body heat.

I don't know much about making clothes, but it was my understanding that synthetic gear could be made without a "shim", thus making the construction (not counting the fill) lighter. I think the Cocoon gear used to make a claim based on that idea (something like "for this weight, it is actually warmer than down"). Of course, even if you gain a little in construction, you would lose it once you started adding more insulation. In other words, a very thin synthetic might be warmer than a down jacket of the same weight, but once the jacket gets thick, the down is lot warmer. I've noticed that the Cocoon gear is no longer sold with this claim. This makes me wonder if the original claim was unfounded or the jackets are heavier (thus making a down jacket of the same weight warmer).

Brian,

What does the addition of a bivy do for a situation like the one you just described? What about when you are under a tarp?

I too slept on 15' of snow at the base of Mt. St. Helens one winter with my 7 year old. Night time temperatures dropped to 18F with daytime temps peaking around 42. We were in clouds by nightfall. As we were protected by trees, there was not much wind through the night in our 4 season double-walled tent. I had with me a down Marmot Lithium sleeping bag rated at 0F.

I woke up the next morning with puddles on the top of my bag, no visible loss of loft and from the waist down, the top of the bag was covered in ice. I remember feeling cozy, but not hot. There is no doubt I let out a lot of water that night. Mostly from exhaling I am sure.

My 7 year olds bag was a 15F REI Zigzag. It kept her toasty with a synthetic base layer she wore that night. She had no dampness on her bag anywhere.

As far as perspiration goes, I have to agree that one perspires a lot through the night, at least based on how hard they worked to get there. The efforts involved may crank up your metabolism causing more sweating than the next guy with a 15 pound pack.

Just my .02c

P.S. I will say based on that experience alone, I would not trust down for more than a weekend at best with the conditions we were in.

Edited by johnatha1 on 09/20/2007 11:30:36 MDT.

I was in the Pecos wilderness this June when we had a sudden downpour followed by 3 inches of hail, followed by more rain. The humidity went from low to 100% in an hour.

My nice double walled tent, sans vestibule, with two of us trying to stay dry during the night, turned into a condensation trap.

My Down bag was soaked by 11:00 pm and the temperature dropped to the high 30's. I was in trouble and knew it.

I managed to scrape together enough semi-moist wood, that with my emergency Esbit tab and a cotton tee shirt that I had packed for hot temps (cotton tee shirt strips make GREAT tinder for a fire), I managed to get a fire going in spite of the wet ground. It took amost every trick I knew, however, to keep that fire going until the moist wood managed to dry out enough to burn well.

I stood around the fire, with my poncho on and pulled up in such a way that I could dry my bag while keeping the rain off.

My son, who I shared the tent with, had an old north face 20 degree synth bag and even though that synth bag was in the same exact moisture laden tent, he stayed toasty all night long.

I'm rethinking my sleep system and for one thing, the double walled tent is out once and for all. I'll stick with my tarptent, which, by the way, my other son used in the same conditions without a problem in the world, or my tarp and I'm going to carry my Bivy with me even if I'm in a tent.

Rethinking the whole sleep system, I'm considering a more layered approach such as the one that Backpackinglight sells.

I've used a 40 degree ray way quilt with a bivy down to freezing before without much problem. It's surprising how much warmer you sleep in a breathable bivy and how much moisture you keep off your bag.

I dont know, I have been in tarptents with crazy condensation which wetted my down bag and I was always just fine and my body heat dried it out eventually.
I am suprised by the difference between your down bag and a synthetic in that situation?
As for winter use of down, I am no real winter hiker but I always thought that a vapour barrier was almost mandatory for any extended use in winter conditions regardless of insulation used?
And just too note Im not saying synthetics dont have an edge in wet conditions, just that down is not quite the cotton of insulations some seem to make it out to be.
I also have a Ray-way quilt and really liked it but for the fact that I made it a bit to short!
But my down quilt stuffs too almost half the volume, has at least an inch more of loft, and wieghts a lot less!
Worth the little extra care in most cases in my opinion.

>I have been in tarptents with crazy condensation which wetted my down bag and I was always just fine and my body heat dried it out eventually.

I think that this discussion highlights the source of a lot of the "conceptual disconnect" sometimes experienced when hikers talk about gear+situation.

I had the fortune of learning to camp in the Rockies and Foothills of Alberta. (North of Montana; probably similar climate.) Spectacularly dry is an understatement: anywhere from freezing to -40 was very safely weatherable by our poorly-equipped scout troop wearing cotton clothes and 80's era jackets in rental sleeping bags and worn-out 70's tents.

Then I moved to the West Coast in my 20's and have been slapped silly by the climate on a few occasions. I weigh 185 and I have a high metabolism and suffice it to say that I never *ever* had a problem keeping warm in Alberta. All the way to -40, even as a skinny teenager, I was never cold. (I was famous for wearing shorts to school in -20C/0F weather.)

Out here, to contrast, I can be bundled up and walking in 5 above zero weather, shopping downtown, and get chilled like a vegan 12-year-old girl with an eating disorder. What the??

If you'd asked me when I lived in Alberta, I would have told you "yeah you have to be more careful with down, but if you get it wet it will always eventually dry with body heat." But my perspective was changed by winter rainforest hiking. In Alberta, the aforementioned statement may generally be true. Out here? Maybe 1/2 the time, if you're smart and careful and have some luck on your side. Some Olympics/Cascades hikers will probably back me up on that.

My point is that our perspectives are often shaped by our "home stomping grounds." As Brett said, it comes down to METTT -- and all broad generalizations should be qualified by location, season, and conditions in which they apply.

Is a bag with 1" of synthtic loft equally warm when compared to a bag with 1" loft of down?

The short answer is "generally not". A high quality 800 fill down bag provides up to 63% more warmth per inch than the AVERAGE synthetic insulated bag. The BEST synthetic insulation on the market provides approximately 30% less insulation per inch than the best 800 fill down bag.

There are a large number of different synthetic insulations. There is also a broad spectrum of down quality and bag construction quality. There can be many exceptions to the general rule.

>Is a bag with 1" of synthtic loft equally warm when compared to a bag with 1" loft of down?

Call it heresy, but I don't place any stock in the standard line that loft=warmth.

The two are strongly correlated, *all things being equal*. But all things are *not* equal.

When it comes to sleep systems, the cut, face fabric, and user's sleeping habits combine with loft measurement to determine the total warmth of a system. I've slept in 2.5" loft bags that were warm for me, and 2.5" loft bags that have just about frozen my balls to the ground a few times. (I have one of each hanging in my bedroom.) The difference has to do with draft control (I move a lot) and cut -- *for me*.

I don't think that you can find two otherwise identical bags or garments that have down/synthetic fill as their only differentiator. Thus, comparing loft directly between synthetic and down-filled garments/bags is necessarily comparing apples to oranges. Or something.

Edited by bjamesd on 09/20/2007 20:24:57 MDT.

Re: " (I have one of each hanging in my bedroom.)" 2.5" loft bags, or balls?

I think the real benefit of synthetics is that you don't have to be as careful with them. My primaloft sleeping bag is a snap to wash and it dries (on air dry)in a half hour. My Polarguard bags take a while longer to dry, but still easier to wash then down. The benefit is you don't have to worry about tearing a baffle or ruining the down. They are low maintenance. If you spill something on them, you know you can clean it pretty easily and not get stressed out like you would with a down bag. If you accidentally tear your fabric (not that there is much of a chance this could happen, but always remember Murphy's Law, it is much easier to repair a synthtic and you don't have to worry about insulation floating all over the place.

Sure synthetics might insulate better when wet, but I have never been in a situation where the bag got soaked. I guess you would have to maybe worry about it if you have a Black Diamond tent, but otherwise you should be alright.

Wow, now you all have me worried. I'm getting ready to make my first sleep system (similar to the Warmlite system, in that it's a "quilt" that is going to zip onto a casing for a downmat), and I've chosen down for the insulation (already purchased, too late to change my mind).

I'm making the shell (both inner and outer) from momentum90, which is said to have a great DWR on it.

I'll be mostly camping in and around New England. While I currently have no plans to use it in winter, I'd like it to be up to the task, and it HAS to work well in the spring and fall. I've got a Rainshadow 2 by Tarptent (good ventilation).

I've only camped in really cold weather once, and condensation was most DEFINITELY an issue. The bag I had at that time was synthetic, and it certainly kept me toasty enough. But I not having had much experience, I had since come to believe the condensation was due to not enough ventilation in the tent (it was a double-walled).

Having researched it (or so I thought), I now understand that condensation also becomes an issue from INSIDE the bag, not just moisture in the tent, and that condensation could still be an issue, even with a well ventilated tent. But then, I also thought that the Warmlite system addressed that as well, by having the entire inner lining of their systems be a vapor barrier...

Therefore I was under the impression that I could keep my down sleep system perfectly functional by having a vapor barrier lining that I can add to the system in the cold, using a DWR shell (so it's breathable, instead of waterproof, therefore not keeping humidity IN, if it DOES get in), and by making sure I have a shelter with little chance of condensation problems (preventing condensed water from dripping onto the OUTSIDE of my DWR-coated bag). I thought I had all my bases covered.

So, my question is, what other down failure stories are out there? And what do you think could have been done differently to avoid the problem (if anything)? Someone earlier asked how a bivy would have helped in some of these situations.

I guess I'm a just a worrier, but you guys really have me all freaked out now about using down. In situations where there's lots of moisture and not much you can do about it, is a VB lining and keeping the outside of the bag dry usually good enough to avoid disaster?

Edited by cowboisgirl on 09/22/2007 23:13:07 MDT.

I think that your greatest fear should be situations in which your VBL does *not* apply: that is 20F below freezing or less.

If it's cold enough to break out the VBL, it's probably cold enough that the air will hold very little moisture. Also, at that temperature your perspiration can be very well-controlled and your VBL will keep it *out* of your insulation. Any excess humidity will generally create frost on the shelter walls, which may or may not rain down on you depending on the shelter you're employing.

Down will pose more of a danger at *warmer* than about 15 degrees F. At these temperatures, you won't comfortably be able to deploy your VBL but it is of course still quite chilly out. In the absence of VBL, moisture evaporated from your skin will pass into your sleep system -- and probably freeze before leaving.

That said, how many nights do you plan to spend at these warm-but-not-warm-enough temperatures? Will you be able to dry your sleep system at all during the day? Will you be wearing warm clothes inside your quilt that you'll be able to dry during the day?

Points to consider.

Brian

> I think that your greatest fear should be situations in which your VBL does *not* apply: that is 20F below freezing or less.
I think you mean 20 F below freezing or WARMER?

Vapor Barrier Clothing will be more functional, more effective, and more flexible (in your sleep system) than a Vapor Barrier Liner inside of your down sleeping bag. You will be able to have a tighter fit with the micro climate next to your skin. You can wear less clothing and not have the perspiration enter your clothing or your sleeping bag.

You will need to experiment with the amount of clothing that you wear outside of your vapor barrier clothing though.

In my case I have opted for 2 Feathered Friends eVENT outer 800+ down sleeping bags in addition to a Cocoon UL60 Polarguard Delta synthetic fill.

I will need to experiment with the eVENT (waterproof breathable) outer sleeping bags under different conditions. But these bags should by all rights be less prone to the problems of down collapse due to condensation inside of my Six Moons Lunar Solo enhanced tent or my Integral Designs tent. Hopefully in those cases where I want to dry out my clothing while I sleep they will be breathable enough so as to let the moisture through and not collect in the down.

Rich

Edited by naturephoto1 on 09/23/2007 05:10:24 MDT.

Sharon,

I have done a fair amount of winter camping in New England and exclusively used high quaility, fill and shell, down for my sleeping system with no adverse results.

Now, let me qualify that statement with two points.

First, I use a tent, not a tarp, so external wetting like spin-drift is not an issue. The tent I use is a Hex3 tee-pee that has top vents and can be set up off the ground/snow all around the perimeter for ventilation. That tent has a high interior volume which I think helps with speading out the humidity (from my breath, etc.) in the micro-climate of the tent. Lastly, the very steep tent walls drastically reduce the amount of drips of condensation that are more of a concern with tents with flatter roofs.

Second, I am only out for 1 to 3 nights, usually not more than 2 nights. A major long trek or thru-hike is an entirely different animal, (unless perhaps you are in a dessert). I do not, and probably never will, have the credentials to address those conditions.

Edited by mad777 on 09/23/2007 10:56:38 MDT.

Yeah, the planned use of my sleep system is going to be mostly for 2-3 day outings (so, 1-2 nights), and not usually (if at all) for flat out winter camping. Though, obviously, I would like it to be useful for longer/colder trips as well.

I'm mostly concerned about all of that unpredictable weather you hear about people encountering up in the mountains - not so much mountains in New England (though it happens here too), but more so about say, in the Rockies or in the Cascades, since I eventually plan to live out that way again.

My Rainshadow 2, well, I haven't had it long enough to test it, but from what I've read, it's good with condensation. There's not much flat space on the roof, and it pitches fairly tautly, with steep enough sides that I don't anticipate dripping to be an issue, especially if I keep a watch on the tautness of the tent when humidity changes...

And not to get too risque, but with regards to VB clothing, and sleeping in it - well, I tend not to like to sleep in anything (clothing gets all tangled up around my legs and arm-pits, etc), and while I can imagine accepting that I may have to sleep in SOME layers in the cold to stay warm enough (or to avoid having to get dressed from a naked state in the morning), I think it would be much harder to adjust to sleeping in VB clothing (as opposed to say, wool or capilene). So I guess my question is, does VB clothing really offer substantial advantages over a VB liner (which wouldn't get all tangled up around me like clothing will)?

********
Edit: Ok, gave the VB clothing thing more thought. Seems like it DOES offer lots more flexibility: say for example, I have a sleep system that keeps me comfortable down to 0F, without any clothing used, but freak weather drops the temp down to -10F or -20F. If I had VB CLOTHING, I could safely add insulating layers, like a jacket, over my VB clothing, to increase insulation, without being in danger of soaking the extra insulation (since VB is next to my skin). On the other hand, if I have a VB liner, any insulation I need to add could get soaked because the VB liner is now keeping the humidity in with me AND my extra insulation.

Sorry - didn't mean to be slow to catch on there.

Guess that means one less zipper I need to worry about incorporating :-)

That said - is there any VB fabric/clothing that could vague feel like pajamas? Somehow I doubt it...

Edited by cowboisgirl on 09/23/2007 22:11:28 MDT.

Wow, there are alot of discussion points in this thread...

I just wanted to add that VB clothing may decrease your prespiration from entering the bags insulation, but that is the least of my worries.

The ability to wear all my clothing in the bag, including my parka, is essential below freezing. It is the moisture in baselyers, shells and parka that concern me... even with VB clothing, that will be pushed into the down.

Also, far and away the biggest problem I have below freezing is my breathe condensing/freezing on the shell around the hood and collar of my bag. This soaks right through Quantum (my experience, every time). A bivy helps this sometimes... but not always.

I honestly think the best system is a down bag and a synthetic overbag- protects from external mositure, yet also places the dew point farther from you, hopefully into the synethtic top. I am seriously considering making a quilt for over my WM Antelope for below zero.

Any experience with this kind of thing?

I have no first hand experience with it but there's WarmLite's "Fuzzy Stuff" fabric. www.warmlite.com

Hi Sharon,

Stephenson's Warmlite makes reasonably priced vapor barrier clothing with fuzzy stuff lining which helps to absorb much of the perspiration and makes the clothing more comfortable against the skin.

Here is a link:

http://www.warmlite.com/vb_shirt.htm

Here is their pricing page link:

http://www.warmlite.com/prices.htm

Rich

I have considered this idea of a synthetic quilt over a down bag in the past. The theory that prespiration vapor might condense in the synthetic vs the down is quite plausible. Though the results would vary in fact given specific circumstances of temperature and humidity, this system should improve one's chances.

I've considered the disadvantage of this system to be the extra weight and bulk caused by 1. synthetic insulation and 2. extra layers of nylon.

One more possible disadvantage is that I can picture myself in a Harold Lloyd / Buster Keaton type silent movie as I try to get into my sleeping bag while keeping the quilt over me and continuing to do so as I toss and turn during the night! (But, that might be due to my coordination level)!

I have concluded that it would be more efficient to simply bring a little higher loft, down sleeping bag in questionable conditions than what would otherwise be called for. A little extra down doesn't weigh much or increase bulk much.

On the other hand, I have a thin synthetic quilt that I made for summer camping, so this dual system wouldn't cost me anything! Hmmm..

Note: My viewpoint is from a 3 day trip as opposed to a thru-hike where minor moisture gained each night can accumulate to something significant.

Edited by mad777 on 09/24/2007 10:54:45 MDT.

Brian - Relative to Ryan Gardner's question, "Is a bag with 1" of synthetic loft equally warm when compared to a bag with 1" loft of down?

I answered his question using ASTM, C1518 derived test data. This procedure eliminates all of the variables that you mentioned.

Edited by richard295 on 09/24/2007 20:36:01 MDT.

Richard,

Ayce over at Thru-Hiker has said that for equal warmth, he would expect that down to be loftier than synthetic clothing, i.e. synthetic insulation is more warm per inch. (See the thread titled "5oz XP rating of 20* with only 1.2” loft?" under the second page of posts in Gearmaker's lounge.) However, you seem to be claiming the opposite. What data are you looking at or how did you arrive at your conclusion? I'm not taking a side here -- just confused about what seems like a discrepancy.

Thanks -- interesting discussion.

Harold – You asked, “What data are you looking at or how did you arrive at your conclusion?”

I have read posts by Acye in the past. In general I was 99% in agreement with him. He not only understands this subject extremely well, but he also does an excellent job of simplifying his explanations. Ayce said, “The problem of including down in these insulation discussions is that it’s a loose insulation of different qualities and can be stuffed to varying degrees. But assuming a company with responsible temperature ratings, if you compared the loft of similar down and synthetic bags with equivalent temperature ratings the down bag will always be loftier.”

My analysis was that a reputable manufacturer will fill the baffles on a down bag to the density that yields the lowest thermal conductivity (same as highest thermal resistance). I knew for example, average quality down, packed to a density of .25 lb/ft3, tests an average thermal conductivity of approximately .32 K in BTUs. By contrast, at increased density levels from about .5 lb/ft3 to 1.6 lb/ft3 tests the same at about .25 K in BTUs. In laymen terms this means the warmest down insulation will have a packing density approximately twice the highest loft/weight ratio down insulation bag. I assumed a reputable manufacture would pack their baffles to yield the highest insulation efficiency... not just the illusory efficiency derived only from loft. My guess is that Acye assumed that they would pack their baffles to yield the highest loft/weight ratio rather than efficiency/weight ratio.



The best compression density packed 800+ fill power down typically tests at .025 and I used that conservative number in my analysis. Some Guarded Hot Plate tests yield as low a conductive value as .020. The following is a representative public domain Guarded Hot Plate .025 W/m K thermal conductivity value for goose down.

Guarded Hot Plate W/m K Values

To calculate the 1" m2K/W thermal resistance of goose down from the Guarded Hot Plate .025 W/m K value, I did the following:

1. I took the reciprocal of the conductivity to calculate the resistance for a 1 meter thick block of insulation.
2. I then multiplied that value by .0254 to determine the thermal resistance for 1”
3. The resultant 1" m2K/W was 1.016

I knew the clo per oz for Primaloft One was .84. I knew 1” of Primaloft One weighed 6 oz and so .84 * 6 = 5.04 clo for 1”. I converted this value to 1" m2K/W by multiplying times 0.15482 to yield .780.

I then divided 1.016/.780 = 1.30. The 1” of optimal density goose down is 30% warmer than a standard Primaloft One 1” bat.

Edited by richard295 on 09/25/2007 00:04:49 MDT.

Richard,
Fascinating chart, and it is making me re-think my concepts of insulation fill. I thought the dead air with its low thermal conductivity was the key ingredient in thermal efficiency of a static system, and down or synthetic fillers only job was to fluff up the layer to maximum loft.
But, your chart and explanation shows that packing more down, past the peak loft/weight ratio, does not improve the loft, but *does* inprove the thermal insulation. What accounts for that? Is that because the additional down reduces the motion of air? Or because down has a lower thermal conductivity than air? Thanks!

Richard - On AYCE's Message Board he responds to a question by saying that commercial bags are typically overfilled by 20%
Ron

Richard,

Reading all of that (and opening up that awesome Power Point presentation) made me feel like I was back in college. Oh wait - I'm at college right now - and my class starts in 15 minutes!

P.S. Keep it coming - this gives me the needed motivation to study my calculus, physics, etc...

Richard,

Thanks for the very clear explanation.

One thing I might argue is that by "maximum efficiency" on this board we usually want to maximize versus weight, not thickness. Compare the points marked "maximum loft" (.32 btu in/hr ft^2 deg F for .25 lb/ft^3) and "maximum efficiency" (.25 btu in/hr ft^2 deg F for .5 lb/ft^3) on your graph. For an equal area and total weight of down, the "maximum loft" will have twice the thickness, and so the heat transfer through the "maximum loft" density will actually be less than that of the "maximum efficiency" density (.32/2 < .25). So to minimize weight (amount of down) we would want a bag or jacket stuffed at what you call "maximum loft" density, not "maximum efficiency".

If we use the "maximum loft" numbers instead of "maximum efficiency", then assuming the ratio is .32/.25 for conductivities, we get something like 0.8 m^2 K/W for 1" of down. This is close to the value you calculated for primaloft one, indicating about similar warmth:loft ratio for down and Primaloft one.

To be thorough I note that thruhiker.com lists 6 oz of primaloft _sport_ having loft of 1.2" and clo of .74. This would give .57 m^2 K/W for 1" thickness. Thruhiker's Climashield XP specs yield .53 m^2 K/W for 1" thickness. Both are less than that of either density of down.

After all these comparisons, it seems that if you use the test numbers you supplied for the conductivity of down, the down will be less lofty or at most a similar loft to equal warmth synthetic. However, AYCE's claim is based on real world experience with his garments -- making me wonder if something is amiss with the calculations.

For example, if we take the following of Ayce's comments from that thread:

"Or compare two of my own kits: the Maxima and the Whitney. These are equivalent jackets, the Maxima being the synthetic version of the Whitney. They are both about the same warmth too: over three years use with the Whitney and two for the Maxima they’re comfortable for me in the 30’s just sitting around. The Maxima has a 3.0 oz basis weight layer of PL Sport with a single layer loft of 0.6” (clo: 3.0 * 0.74=2.2) while the Whitney fully lofted has on average about 1.5” of single layer loft. In other words, the synthetic jacket is as warm as the twice as lofty down jacket."

then it means that 1.5" of down loft has clo of 2.2, or for 1" of down 1.5 clo or .23 m^2 K/W -- a factor of 4 or 5 different from your calculation! I wonder what is causing such a large discrepancy...

Edited by huppy on 09/25/2007 09:21:06 MDT.

Brett - Synthetic insulations comes from the factory with a fixed density to optimize its conductive, convective, and radiative heat losses. Down has variable density depending on its fill power and its density in the baffles.

Natural convection heat loss is negligible even at the lowest down density (highest loft). The conductive heat loss is dependent on the thickness of the insulation and so the thicker the insulation the less the heat loss. Radiative heat loss is decreases with higher bulk density up to a point. The optimal design of down baffles is a sweet spot just before the point where further increases in density, to offset radiative heat loss, occur at the expense of increased conductive heat loss.

Ron - A 20% overfill should yield the maximum thermal efficiency potential of down. According to my calculations 800 fill goose down, at this density, will be warmer than any synthetic insulation on the market. I am at a loss to explain why Ayce said that a down bag would have to be thicker to achieve the same warmth as an average synthetic.

Harold - Set the thermostat in your house to 70F. Set a heating pad to its highest setting. Use your own jackets or borrow some that are close to what Acye tested. Put the jacket over the heating pad. Put a thermometer on top of the jacket being tested. Wait a few hours for thermal equilibrium to set in and then record the thermometer reading. Do this for each jacket you have. The jacket with the lowest temperature on top will have the highest insulation. This simple home test won't tell you the insulation value, but it will give you an unbiased independent assessment of the relative warmth for each garment.

5/25/07 Simple Home Test Experiment:

New Balance Fugu (800 Down 1.5")
Cableas Jacket (650 Down 1.5")
Wild Things Jacket/Vest-Red (Primaloft1 1.2")
MEC Magma Jacket (Primaloft1 1.2")
Wild Things Primaloft Jacket-Red (Primaloft1 .6")
Wild Things Primaloft Vest-Red (Primaloft1 .6")
MEC Magma Pants (Primaloft1 .6")
Patagonia Micropuff Vest (Polargaurd Delta .6")
Patagonia Micropuff Pullover (Polargaurd Delta .6")
Patagonia Micropuff Jacket (Polargaurd Delta .6")
Wild Things Primaloft Jacket-Yellow (Primaloft1 .6")
Wild Things Primaloft Vest-Yellow (Primaloft1 .6")
MH Polartec 300 (.250")
Patagonia Black Puffball Vest (Thermolite Micro .156")



% of ideal is the ratio of the ambient room temperature / jacket top temperature

The Fugu down jacket is 800 fill and the Cabelas down jacket is 650 fill. They are sewn through construction. 1 1/2" is the maximum loft. The baffles average 5" wide. Only approximately 2" of the 5" is at the maximum loft. 1 1/2" on either side it ramps up from a few mm to 1 1/2". My crude estimate is that the average loft is about 70% of the max or 1.05". This compares to the Primaloft One MEC and the Primaloft One New Wild Things vest and jacket combination. Considering that the effective lofts are comparable, both down garments displayed significantly higher thermal resistance than the best synthetic on the market.

The yellow Wild Things Primaloft jacket / vest had been used on two multi-month expeditions and had been stuffed daily. The red Wild Things Primaloft jacket / vest is new.

Edited by richard295 on 09/25/2007 15:19:20 MDT.

The most striking observation to me is not so much the graph, but how much loss of insulative value the primaloft jacket suffered.

Richard,

I'm glad you did that experiment. An experiment is worth many many calculations.

With a little additional information, your home test should be quite convincing for ballpark numbers -- certainly enough to resolve between the factor of 4 or 5 differences between claims. Do you know the approximate temperature of the hot pad? If the hot pad control setting fixes the power output and the geometry in each case was roughly the same (or, if you lay the garments flat on the pad, and you assume the power output of the pad is evenly distributed over area), you can obtain relative R values for each garment by calculating the temperature gradient.

Is it correct to read from your graph that the temperature on top of the fugu piece was 70 deg/.93 = 75 deg F, and on top of the WT vest or jacket 70/.81=86 deg F? Or did you use deg C, or K for temperature units?

If the heat pad temperature is around 110 F, you have temperature gradients of 35 degrees and 24 degrees, respectively, for down and .6" PL -- so the 1.5" down is about 1.5 times as insulating as the .6" PL (2.2 clo). That is about 3.3 clo, closer to Ayce's experience. If the hot pad temperature is lower, say 90 deg F, then you have temperature gradients of 15 and 4, and the down is about 8.25 clo, closer to your calculation.

Lots of assumptions here, but it seems like we should be able to get within a factor of two.

I'd like to do this test myself -- but I don't own any down garments!

Richard,

You never cease to amaze me! That "home test" is fantastic. As Harold has asked, if you could fill us in on the temperature of the hot plate and the ambient room temperature, that would further put this in perspective.

I also noted with interest the diffence between the well used vs. the new Primaloft garments.

Keep up the good work and thanks!

Harold - All measurements were in F and the ambient room temperature was 71.7F (thermastat was set to 70F). The test area was free from major radiant heat sources (windows & heating vents). The hot pad I used was the Sunbeam Sports Wrap with Intelligent Controller, Model 902. I used the high setting because it achieved equilibrium temp the fastest and regulated the best of the multiple settings on the heat pad. The following is a temperature time plot for the H setting.



The test geometry was the same for all tests. The garment was fluffed and the back was centered over the pad. The temperature sensor was also centered over the pad.

Ideally I would set the heat source for the average skin temperature of 93F. My heating pad provided 91.4F for the 3 setting and 101.3 for the 4 setting. The heat pad's temperature controller did not ramp up and stabilize quickly for either of those settings. The following is the 3 setting plot.

Edited by richard295 on 09/25/2007 15:44:04 MDT.

Daniel & Michael - Primaloft One is one of the worst synthetics for loosing loft / insulation value through stuffing and washing but, all synthetics exhibit that characteristic to various degrees. This is in stark contrast to down’s durability.

Polarguard Delta is one of the best synthetics for durability. Yet, I typically loose 30% loft from a new Polarguard Delta sleeping bag after one season of use. Granted… I use a compression sack to minimize packing space but, I only wash a synthetic sleeping bag once per season.

Edited by richard295 on 09/25/2007 15:35:55 MDT.

"The most striking observation to me is not so much the graph, but how much loss of insulative value the primaloft jacket suffered."

One thing to remeber when looking at this graph is the base isn't at zero. Looking quickly at the graph it seems the primaloft vest and jacket lost over half there insulating ability, but the difference is only from just over 81% of ideal to just under 79%. Since the temperature differential was 65 deg F, 2% is only about 1.3 degrees difference in thermometer readings.

Richard,

Thanks for the details of your home test. From your description ("Intelligent Control" and temperature graphs), it sounds like your heat pad may not output a constant power but instead regulate to a fixed temperature. If the power output varies by a lot, my estimates of relative thermal conductivity may not hold. Without knowing those properties of your heat pad, ultimately I don't know what to conclude, unfortunately.

The temperature differential between the garment surface and the ambient temperature may also give us some useful information about the heat flow, but I don't know enough about heat transfer in air to make any statements regarding that.


James,
Good point about the relative scale for insulation degradation. This seems to indicate that even if the garments lose loft (as Richard observed) the thermal properties are not greatly affected. Does this match with subjective experience?

My 1st down garment was The North Face's first heavy down parka in the mid '70s. I sold it right away after getting the back soaking wet while backpacking in -5 F temps. Went to an Alpine Designs (remember them?) synthetic parka & was very happy.

Down is Ok for camp use and ice fishing or promenading at Vail Village or your local haute coture store. REALLY good down (i.e. 800 fill plumules from mature birds) is necessary for extreme mountaineering due to weight savings.

Eric

That is a very cool test and a great starting point, but I think the differences in temperature from what we experience in the woods vs. ambient temp of a house and differences in hotplate temp and heat emitted by a sleeper may skew the results a bit. Here is my reasoning:

From what i gather, by comparing the fugu and the jacket/vest with 1.2" primaloft, the primaloft insulates about 90% as well as the 1.5" of down with 80% of the loft. Thats an interesting result which promotes synthetics being better per inch at warmth, but it seems a bit off kilter from 1.2" of primaloft making a 20* rated bag (15* depending on the companies ethics) as reported by several sources, and that also according to several highly esteemed companies, 2.5" of single side loft w/ high quality down makes for the same 20* bag. The difference there is over 2 times the warmth for the same loft as down. It is also similar for other modern synthetic insulations like climashield XP and combat. I would highly recommend people still relying on loft to measure synthetic bag warmth to read up on clo measurements to find the warmth of what they want to make or buy because not all inches are the same.

so if I've understood right, Richard, what you're saying is a given amount (weight) of down per volume unit is more thermally efficient when slightly compressed (by baffle height limit) than if left to loft fully. Is that correct?

And if we compare the best quality down with the best synthetics we should then be using this slightly compressed down for the comparison to be fair and down would still be warmer by around 30%, right?

Let me recall it's the warmth/weight ratio that we want to maximize, nevermind the loft (in case warmth and loft don't have a 1 to 1 relation, which is what's being discussed). I've read too many posts that discuss loft and warmth but don't mention weight. Maybe it's implicit data and I don't know but I guess I don't care if a less lofty synthetic insulates as much as a loftier down item if it still weights more.

Inaki,

I'm not Richard, but I'd like to chime in. I agree that the more important question is warmth/weight. However, the question of warmth/loft is important if we want to compare the warmth of a down garment and a synthetic garment, with the ultimate goal of then comparing the weights of equivalent warmth down and synthetic garments so we can evaluate the trade-offs.

From this thread, I feel there is no settled consensus on how to compare the clo values of a down garment with a synthetic garment of known fill material. A rough ballpark estimate could be made if we knew the relative warmth/loft of down, but there seem to be contradicting experiences and facts regarding this (Richard's quoted thermal conductivity of down vs Ayce's experience and David's observations on sleeping bag ratings).

Finally, in regard to how densely down should be packed, I tried to make the point above (not very well, I guess) that it still makes sense to pack down for optimum loft, the reason being that even though the "k" value Richard listed is higher (more heat conduction, worse), the overall insulating power (which goes as thickness/k) is better for the same amount of down, because the less densely packed down is twice as thick.

Yikes! My head is starting to hurt!

Are we saying that a 1" thick down garment, that is stuffed to allow the down to reach its natural loft, when compared to a 0.8" thick garment using the same weight of down, therefore compressed by 20%, that these two pieces would be approximately, equal in warmth and would weigh about the same, minus a little due to shorter baffle height?

I can't find it now, but there was an article by BPL about 3 years ago, comparing high loft down jackets. As I remember, the reviewer remarked that the Rab Neutrino (which is sewn thru) felt warmer than the jackets that had baffle construction. The reviewer attributed this to the Rab being over-stuffed. That article would lend credence to this idea.

Edited by mad777 on 09/26/2007 10:46:28 MDT.

Harold, your previous explanation was fine and your conclusion seemed logical to me. I know I may be missing something as I don't fully know the meaning of these K value or the units involved (ok, it's heat conduction, less is better... but I don't know if the variation is linear with the weight/thickness/density). Then I was expecting Richard to clarify the discrepancy and he answered your message but not this question so I was asking again.

Richard, you provided very interesting info in that answer to Harold but unless I'm missing something this question is yet open. And since it seems clear that higher density down has a better warmth/loft ratio, it seems pretty useless to even try to compare warmth/loft between down and synthetics if we don't settle on which down setting first.

I really hope what I'm saying makes sense and I'm not complicating things further. If I am, please tell me to shut up :)

Here's an experiment I did last weekend tetsing down vs synthetic bags.

Conditions: It snowed about 3 inches, of which 1-2 melted. We were by a steaming lake (probably 50F compared with the ambient temperatures of 35F in the day and 26F at night). Thus very humid and fairly cold but not deep cold that sucks the moisture out of the air.

Gear: For the weekend I used a dual quilt system: a custom 13oz Nunatak bag with 2-2.5" of loft under a Cocoon 180 with 1.5" loft. I used a bivy sack and camped in a Black Diamond Mega-light.

Procedure:
7:30pm--go to lake, remove pants, pile hat, pile sweater, pile gloves and submerge till soaked in lake. Wring out until no more water dripped from clothing but not as dry as it could have been with further wringing. Put clothing on over wool base layer and medium weight capilene. Remain at fire an hour while "dripping" a bit. Still quite wet at the end.

8:30pm--Removing clothing except light base layer, put vapor barried clothing on over the base layer, put all wet clothing back on. Socks now soaked from water dripping from pants. Go to bed. [Vapor barrier clothing used to help separate clothing from body moisture issues and to further test VB clothing in warmer conditions.]

In the morning clothing had mostly dried. They were still moist but comfortable--I changed out of the vapor barrier and back to the (previously) wet clothing. The night was comfortable but the bag was very moist.

At home I weighed the bags and measured their loft before and after drying.

RESULTS:
Nunatak down Cocoon 180
Pre-Drying
Weight 14.4oz 19.7 oz
Loft * 1.25" 1.125"

Post-Drying
Weight 13oz 17oz
Loft * 2.25" 1.5"

Loft Lost% 45% 25%
Weight Gained%10% 16%

*It is very difficult to accurately measure loft--I fluffed both bags, placed them on a wood floor, held a yardstick on the surface so most of it touched the bag (two measurements side to side, one top to bottom with the three results averaged) From here I pushed a ruler down vertically until it hit the floor (compressing the material) and read the measurement against bottom of the yardstick.

I wasn't surprised that the down lost so much loft. I was surprised that it lost so much loft despite having gained less water weight. The synthetic bag gained 50% more water weight, but lost only half loft of the down bag. Interestingly, even after a very wet night the down bag still weighed less and provided more loft than the synthetic. However with another night out in similar conditions the trend wasn't promising.

Based on this test as well as the difficulties keeping two quilts aligned and closed as I turned from side to side as I slept, I would bring a synthetic bag in conditions such as we faced on this trip. (moist/cold when clothing is likely to get wet).

I've had good results using vapor barrier clothing and down in the winter (below 30F) when clothing doesn't generally get wet. I'd like to experiment with using VB clothing in moist above freezing conditions when I'm sure I can keep my clothing dry.

Harold & Inaki – If you opt for 800 fill down baffles filled for optimal thermal density, they will out-perform (>oz/inch/yd2-green, >clo/in/yd2-red, >clo/oz/yd2-blue) the best synthetics when dry. If you opt for max loft only, you will have better oz/inch/yd2-green (eye candy) but you will not have a higher clo/oz which is the most critical measure for backpackers. I cannot quote you the clo/oz for the lowest density because I am not aware of any labs that have published W/m K values for sub optimal thermal down densities.

My simple relative performance heating pad test demonstrated the same relative results as this spreadsheet. The down garments are warmer than the new Primaloft One garments of comparable thickness (average down baffle height rather than max down baffle height).




I created the above spreadsheet for use in this post. Down is very complex to compare with synthetics because of the variables: down loft and down bulk density. I attempted to focus on just one representative down combination to simplify its comparison with synthetics.

Edited by richard295 on 09/26/2007 18:09:23 MDT.

Michael - The article you referred to was entitled, "Winter Backpacking Comfort: Lightweight Gear and Techniques for Shelter, Clothing, and Sleep Systems"

It said in part, ..."The Rab Neutrino has overstuffed sewn-through baffles, a hood, and a full zip. Despite its sewn-through baffling, we found the Neutrino to be warmer than many other down jackets using baffled construction - a testament to the attention to detail and fit that Rab paid to the design of this jacket. For the winter alpinist, this jacket may offer the highest warmth:weight ratio of any insulating jacket available..."

High quality down compressed to the optimal bulk density, is unsurpassed in clo/oz when kept dry. The over simplified phrase "thickness equals warmth" is used because attempting to explain what really equals warmth almost always results in, "Yikes! My head is starting to hurt!”

My prior post with the spread sheet should answer your first question.

Inaki - Yes the variation is linear with thickness. If you double the thickness, the resistance is doubled and conductivity (K) is reduced to 1/2.

.

Edited by huppy on 09/27/2007 06:52:13 MDT.

Harold-I multiplied by 2.5 because the product is the weight in oz. Look up the weight of a 1" thick yd2 piece of Primaloft to see the consistency in this green column. You will find that it weighs 6 oz and 1" thick yd2 Climashield XP weighs 4 oz. Everything in the green column is the weight of a 1" thick sample yd2. Please consider this information in place of your initial assumption and give it another try.



Maybe this graph will make the density factor easier to understand. For construction purposes a material is defined as insulating only if its thermal conductivity is significantly less than 0.06 W/m K. Uncompressed down would not be considered an insulator by most building code standards.

Another way of looking at max loft down with a thermal conductivity of .06 is that each inch of the eye candy uncompressed down equals the thermal insulation provided by the same thickness of dry snow or saw dust. Granted that down is LIGHTER than snow or saw dust but the thermal insulation value is abysmal.

Also note that Primaloft One, also known as Bimodal Polyester Artificial Down, is only offered in battings with a thermal conductivity value of ~.033. All of the less dense green dots above this point could be offered to the market but are not. Is it now obvious why not?

Edited by richard295 on 09/27/2007 10:43:06 MDT.

"Conditions: It snowed about 3 inches, of which 1-2 melted. We were by a steaming lake (probably 50F compared with the ambient temperatures of 35F in the day and 26F at night). Thus very humid and fairly cold but not deep cold that sucks the moisture out of the air.

Gear: For the weekend I used a dual quilt system: a custom 13oz Nunatak bag with 2-2.5" of loft under a Cocoon 180 with 1.5" loft. I used a bivy sack and camped in a Black Diamond Mega-light."

Interesting experiment. It would also be interesting to see what happened if each bag were used separately or if the Cocoon were used under the Nunatak, since whatever passed into the Cocoon in your experiment had to pass totally through the Nunatak.

Hi Richard,

Thanks. You are right; I was being an idiot (although you were nice enough not to say so). You have the density in the 4th and 5th columns. I'm going to edit my previous post so I don't drag others into my confusion.

I'd like to return to the question of clo/oz for the uncompressed down, though. The following from what I said in the post I edited still holds, I think:

When you say you do not know any values for W/mK for
suboptimal density down, you seem to ignore the first
graph you posted in this discussion. There you have .32
btu in/(hr ft^2 deg F). The conversion to W/(m K) is
multiplying by .144, so the max loft density down has
(granted, for "average down", and not 800 fill) a .046
W/mK and the "max efficiency" density down has
.036 W/m K. I thought it was reasonable to infer from
this that the optimal loft 800 fill down should have a
clo/in of 6.562*.036/.046 = 5.13 clo/in. Or do you
believe that 800 fill down has a markedly different
compression-dependence of thermal conductivity than the
"average" down so we cannot infer this?

If we use the value 5.13 clo/in for uncompressed down, we find that the clo/oz is 5.13 / 1.62 = 3.2 clo/oz, still higher than the compressed down.

In the last graph you posted you also have data on thermal conductivity vs down density. If you present that data on a scale where we can see the bulk density for each data point a little more clearly, we can find the optimum density by maximizing the quantity
1/( [Thermal conductivity (W/mK)]*[density kg/m^3] ), which is proportional to clo/oz. Or you can just plot that quantity vs density. These data may show that there should be some compression to optimize clo/oz, but the data in your original chart (with the points at .32 btu in/hr yd^2 deg F for .25 lb/ft^3 down and .25 btu in/hr yd^2 deg F for .5 lb/ft^3 down) clearly shows the least compressed down has the best clo/oz.

We can do the same thing for the bimodal polyester (PL one) data. Then we can find out if the .033 w/mK batting has optimized for clo/oz.

Incidentally those data also tell us the quality of down measured -- for example 800 fill down at max loft has a density of 2.16 kg/m^3. The first graph you posted had a minimum density of .25 lb/ft^3 which corresponds to 430 fill down.

I don't think that what building code standards require are necessarily applicable, because they care about how thick the insulation is (presumably because it takes extra material to build thick walls to hold that insulation). Hence thermal conductivity in W/mK, or the resistance clo/in (both are normalized to thickness) is important. In garments and sleeping bags the thickness constraint is not as important (because extra thickness is just making wider baffles), and we care about clo/oz (normalized to weight).

Edited by huppy on 09/27/2007 06:54:00 MDT.

I had been meaning to do this after my last post, but was traveling yesterday. Using the data from the graph in Richard's post on 09/24/2007 23:08:15 MDT, I have plotted the clo/oz values for down at various compression. From the minimum density, I estimate this down to be 430 fill.



The least compressed down has the highest clo/oz.

The numbers used are in the following table:



In this table, columns 1 and 3 are read off of Richard's graph. Column 2 is derived from column 1, while columns 4 and 5 are derived from column 3. Column 6 is column 5 divided by column 2.

Edited by huppy on 09/29/2007 14:06:43 MDT.

With the Vapor barrier liner of suit is a dedicated set of undies needed of does it go next to skin.

I hate crawling out of my bag at -5, it would especially be bad with damp skin or skivies.

Would a vapor barrier shirt alone provide enough moisture protection?

So Harold,

To make sure I'm applying the information in your spreadsheet correctly to real world applications, I offer the following example:

Using your numbers and, assuming that we only care about weight (not bulk), then we should be constructing garments to allow fully uncompressed loft of the down.

For example, if we were to construct a vest using 3 oz. of down, such that it would fully loft, the garment might be about 1.5 in. thick (depending on size).

If we made that exact same size vest with the same 3 oz. of down but made it only 3/4 in. thick, it would not be as warm as the thicker vest, even though the same amount of down was used. Right?

Michael,

Yes, from the data that Richard generously shared with us, I would draw the conclusion that your garment with 3 oz of down would be warmer if it is built to allow the down to fully loft than if it were built with narrower baffles.

The final garment weight would include the extra weight of wider baffles. My guess is that that wouldn't add enough to change the conclusion.

Right now, this only includes the data from Richard's first post, which apparently was made using quite inferior down (430 fill). I would expect similar to hold true for, say, 800 fill down, but that is only my opinion -- I have no data to back it up. If Richard shares with us his data from his last post, or plots it in a way where I can see the values,
I'd be happy to add those data points to the picture.