Exped Synmat UL 7 felt "cool" under hips at 5-8 deg C
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Matt Purnell
(Treefern)

Locale: Brisbane
Exped Synmat UL 7 felt "cool" under hips at 5-8 deg C on 05/19/2013 22:01:55 MDT Print View

I’ve just bought and tried out a Synmat UL 7 medium. Unfortunately it felt “cool” under the hips. I was camped on bare ground with the PU floor of the tent in between. The air temp was somewhere between 5 and 8 deg C. I was car camping, so I was in my warm tent and warm sleeping bag and my body was otherwise warm. On a hiking trip I’d have the same situation, except the tent floor would be silnylon and the air temperature could be a little colder – somewhere between 0 and 5 deg C.

So a couple of questions:

1. Is feeling a bit “cooler” under the hip normal on a relatively thick air mattress? My last mat was a Metzeler Thermo, which one inflated to about 3cm thickness with about two big puffs. I used the schnozzle bag to inflate the 7cm thick Exped – I think I’d pass out if I tried to inflate it by mouth. The mat was fully inflated – a test at home demonstrated that was necessary lest my hips hit the ground.

The sensation wasn’t “cold” – just “cool”. And once asleep this “coolness” didn’t wake me up. I’ve read plenty of BPL testimonials by people saying they’ve had no problems at temperatures lower than I’m reporting. Has anyone else experienced this sensation at these temps and just puts up with it to save weight?

I was wearing only a pair of boxer shorts and a t-shirt. If I was also wearing woollen leggings and nylon pants, might that make much of a difference?

2. How feasible is supplementing the warmth of the mat with a short section of thin closed-cell foam that just goes under the hips? Otherwise it’s the Exped Downmat UL 7 medium for me I think. (I want to stick with Exped because the mat was so comfy.)

However, the weight difference between the Downmat medium (560g) and the Synmat medium (455g) is 105g.

I’d only need a section of foam that’s about 30cm x 52cm. But wouldn’t that approach 95g anyway? For example, a Gossamer Gear large sit pad (25cm x 53cm x 2cm) is 54g (http://gossamergear.com/sleeping/sitlight-sit-pad-group.html).

So, I’m in two minds. I hardly ever camp below 0 deg C, but I get cold easily, my Six Moons Haven tarp + net-tent is airy and “cold”, and I’m planning on replacing my heavy, very warm sleeping bag with a quilt. Should I just play it safe and get the Downmat, or should I supplement the Synmat?

Edited by Treefern on 05/19/2013 22:03:20 MDT.

Randy Martin
(randalmartin) - F

Locale: Colorado
Sleep Clothing on 05/19/2013 22:17:50 MDT Print View

My first reaction is that I would never sleep in boxer shorts and t-shirt. One of the cardinal rules of cold weather camping is to wear at least some of your insulated clothing/base layers to sleep. It not only helps supplement your comfort but also keeps your sleeping bag much cleaner.

I think the idea of putting a small section of thin foam (perhaps dual use as a sit pad or frame sheet) under your hips is an excellent idea in colder conditions.

Todd Taylor
(texasbb) - F

Locale: Pacific Northwest
Synmat UL R-value... on 05/19/2013 22:36:04 MDT Print View

is a little lower than some alternatives. It's a smidge over R-3, which compares to a tad over R-4 for some other popular air pads like the Big Agnes Insulated Air Core. That means the Synmat allows about a third more heat transfer at any given temperature difference, other things being equal. I'm not criticizing the Synmat--I love mine--just pointing out the specs.

Stuart .
(lotuseater) - M

Locale: 40°N,-105°W-ish
'Cool' Synmat UL7 on 05/19/2013 22:45:49 MDT Print View

There are many ways to lose heat at night, and conduction to the ground is only one of them. You mention that your Synmat UL7 was fully inflated - that's good, as the insulation value is a factor of how full the pad is. Is your sleeping bag accurately rated, and is it new / clean? How well does your tent block wind? Did you eat well before you went to bed, and were you well hydrated? What's your metabolism like? Was your site in a valley, near water, or in another location that could have caused the localised temperature to be lower than in surrounding areas?

First time I took my Synmat UL7 out, I made a lot of mistakes. It was early season, my sleeping bag wasn't rated high enough, I was probably dehydrated, and I pitched camp in a valley close to water. Each time since I've made adjustments, and the mat has been comfortable down to ~3-4C. When it's borderline I will add a 1/8" closed cell pad to add an extra layer of insulation. But when I expect temps below -5C I'll switch to my Downmat UL7.

Just don't expect the mat to be a panacea - you have to be mindful of other factors.

Matt Purnell
(Treefern)

Locale: Brisbane
"Coolness" was localized to under my hip on 05/20/2013 00:49:15 MDT Print View

Thanks for the comments so far. Stuart D - yes to all the above. I was car camping, so I was well-fed, well-watered, well everything and using my warm double-walled tent with fabric inner and my sleeping bag rated to -5 deg C. It's not new but it is clean and the reason I sleep in boxers and a t-shirt in it is otherwise I overheat! I had to keep the side zip and the toe-box zip open most of the night. So, my body wasn't cold. But even while feeling otherwise toasty warm, when I lay on my side I could feel "coolness" under my hip, which I'm concluding was either localized heat loss at that point, or my imagination.

Stuart D, when you say "the mat has been comfortable down to ~3-4C", do you mean -3 to -4 deg C, or +3 to +4 deg C?

On a hiking trip (as opposed to this car camping trip) I would be in a "colder" tent, wearing all my layers, and using a quilt. So, if I wasn't imagining things and the Synmat is borderline at the temps I normally encounter (0 to 5 deg C), should I swap it with the Downmat (add 105g), or use a bit of foam under the hips (add ?g)?

BTW, the minimum air temp was likely in the range 5 to 8 deg C with no significant wind chill. The car next to me registered 5 deg C, mine registered 8 deg C, and a thermometer at a nearby house registered 8 deg C.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Exped Synmat UL 7 felt "cool" under hips at 5-8 deg C on 05/20/2013 04:54:14 MDT Print View

UL 7 plus 1/8" foam mat (GG?) down to -7 C. We were warm.

The secret is to NOT camp on a hard smooth surface. If you camp on a lumpy surface (oh the horror!) you can always find somewhere between the lumps for your hips. Then the mat is not so thin.

Cheers

Matt Purnell
(Treefern)

Locale: Brisbane
1/8" foam mat in Oz? on 05/20/2013 06:06:25 MDT Print View

Thanks Roger. Any idea where one can buy a 1/8" foam mat in Australia?

SPIRIDON Papapetroy
(spotlight) - F
Quilt vs sleeping bag. on 05/20/2013 06:25:26 MDT Print View

I was also thinking of a quilt but i have never uswed one yet to see the difference from sleeping bags. My current sleeping bag is Monbel UL super spiral down hugger #3. I think it might feel strange to sleep with my head and arms outside the quilt.

Stuart .
(lotuseater) - M

Locale: 40°N,-105°W-ish
Temps on 05/20/2013 07:06:04 MDT Print View

@Matt - I meant approximately +3C to + 4C. I tend to think in Fahrenheit after the best part of two decades living in the US, so conversions back to Celsius / Centigrade are a little rough and ready.

I typically take a torso length 1/8" closed cell pad with me regardless of temps, as a little insurance against cold and sharp objects. I ruined my first Synmat UL7 with a large scratch from a dog's claw. He didn't slice the pad wide open, but the pad never held air for more than a few minutes after that.

Roger's advice is good, as always.

Paul Mountford
(Sparticus) - MLife

Locale: Atlantic Canada
Re: Re: Exped Synmat UL 7 felt "cool" under hips at 5-8 deg C on 05/20/2013 07:58:39 MDT Print View

+1 to Roger’s recommendation. On the last few trips I have been a little cool on my Big Angus Insulated Core. I was just chalking it up to me being a cold sleeper in my quilt. On my last trip to Scotland some cold temps were projected, so I also brought a torso length InsuLite 1/8" Foam Pad.

As it turns out, I’m not quite the cold sleeper that I thought I was. I made it through -14 deg C night with my quilt and some extra clothing. My son, who is a warm sleeper, over heated almost every night in his golite 20 quilt. Before this trip, I would not have thought an extra 1/8’th of an inch would have that much of an effect, but it certainly did for my son and I.

Colin Krusor
(ckrusor) - M

Locale: Northwest US
UL7 on 05/20/2013 08:58:41 MDT Print View

My synmat UL7 has felt cool under my hips and shoulders at about that temp (0-4 C). On one trip, I remedied that problem by piling a layer of pine duff under the pad to separate it from the cold granite. A thin CCF pad would have worked, too.

Dan Durston
(dandydan) - M

Locale: Cascadia
Synmat UL7 on 05/20/2013 09:32:50 MDT Print View

+1 to Colin

Edited by dandydan on 05/20/2013 09:33:26 MDT.

Andrew Martin
(am1982) - M

Locale: PacNW
CCF for cold ground with UL7 or Synmat 7 on 05/20/2013 11:19:28 MDT Print View

+1 Roger and Colin

I've owned and used both the UL 7 and original 7 with snow camping and some winter non-snow camping. These pads will conduct too much heat from the air-cells into the ground unless paired with thin ccf pads. Torso length works OK and full length is even warmer. My guess is that there is enough air circulation inside the UL 7 that the internal air temp is relatively even throughout. The R-value of the combined system must be substantially greater than either component alone given my experience. I've successfully slept in a 30 degree bag with pad+UL7 on snow multiple nights inside a double-walled tent.

Edit: The weight of thin foam can be easily offset in shelter or sleeping bag weight reduction. Matt you are probably safe to assume that a more airy (lighter) shelter or lighter sleeping bag/quilt will be cozy once you pair your mat up with some foam given how warm you were sleeping without foam.

Edited by am1982 on 05/20/2013 11:32:42 MDT.

Dena Kelley
(EagleRiverDee) - M

Locale: Eagle River, Alaska
RE "Exped Synmat UL 7 felt "cool" under hips at 5-8 deg C" on 05/20/2013 11:23:11 MDT Print View

Had the same experience with my Big Agnes Q-Core SL this weekend. Went camping in about 20°F weather and the Q-Core was significantly transmitting the cold from the ground. I had brought a Z-Rest to top it with, as I had heard this might happen. I was glad I had it, it made all the difference.

Matt Purnell
(Treefern)

Locale: Brisbane
Sources of 1/8" foam? on 05/20/2013 15:29:21 MDT Print View

Thanks all. There's seems to be a clear consensus to supplement the Synmat rather than swap it for the Downmat. I guess this makes sense as the added weight will come in lower than 105g, and the foam will protect the air mattress somewhat, and can be used for other purposes.

Anyone recommend a source for the 1/8" foam? I've seen it here http://gossamergear.com/sleeping/1-8.html, but the shipping to Australia is crazy.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Sources of 1/8" foam? on 05/20/2013 15:58:42 MDT Print View

You can get 1/4" foam at any Clark Rubber shop, in the form of very cheap camping mats. They may or may not have thinner foam.
I imagine you could get such mats at places like K-mart, Target etc, and at tourist camping places like Kellys as well.
Note that there are light foams and heavy foams. Check carefully. Do not buy open cell foam though: it will not work! Only Closed Cell Foam (CCF).

Cheers

Matt Purnell
(Treefern)

Locale: Brisbane
Re: Sources of 1/8" foam? on 05/20/2013 17:49:15 MDT Print View

Thanks Roger.

Kelly G
(KellyDT) - F
1/8th ccf on 05/20/2013 20:00:08 MDT Print View

+1 on the 1/8th ccf. Used my synmat UL7 for the 1st time, probably got to 40*f, and was cool all over. (I run cold!) Added my GG thinlight and ahhhh, made all the difference.
Kelly

J C
(Joomy) - M
Re: Sources of 1/8" foam? on 05/20/2013 22:14:30 MDT Print View

I have a local foam and rubber shop (http://www.actfoam.com.au/) that sells CCF in all sorts of ticknesses from 6mm or less to 10-15mm. Not sure how it compares to the supposedly very good Evazote stuff from GG and other places but I'm sure it's not very different.

Btw I have also been considering the Synmat vs. Downmat option. I had settled on a Downmat but now I think Synmat + 4-5mm foam might be the better more versatile option too.

EDIT: Btw, Exped themselves sell a 4mm Evazote mat which weighs 390g for 2000x1000x4mm. If they import it you could cut that down to 1000x500x4 for roughly 100g. I might go to my local Exped stockist and investigate this option myself.

Edited by Joomy on 05/20/2013 22:27:52 MDT.

Matt Purnell
(Treefern)

Locale: Brisbane
Re: Sources of 1/8" foam on 05/20/2013 22:58:48 MDT Print View

Glad to hear Kelly G that I'm not the only cold fish out there!

Jeremy, I've got a quote for a 2m x 1m sheet of blue EVA30 at 3mm thickness from these guys: http://www.kangarubber.com.au/eva.html. $35 including postage. From my calculations this seems to be a very similar material to the Gossamer Gear Thinlight Pad (http://gossamergear.com/sleeping/1-8.html).

I've also found that arts and craft suppliers stock A4 and A3 EVA sheets at 2 to 3mm thickness, for only a dollar or two. For example, http://www.artworxgeelong.com.au/store/store.php?Eva_Foam_Sheets-pg1-cid265.html

Higher density and hence more weight, but cheap!

J C
(Joomy) - M
Re: Re: Sources of 1/8" foam on 05/20/2013 23:08:40 MDT Print View

Density is the thing though isn't it. If we are talking about maximum weight savings then the GG pads still win, 82g for 1500x500x3mm. Logically, it seems that less dense EVA should be warmer too since it would contain more air, but I'm sure it's more complicated than that.

What's the difference between their EVA30 and the EVA75? And is that stuff Evazote? The black EVA75 looks like it could be...

Edited by Joomy on 05/20/2013 23:16:31 MDT.

Matt Purnell
(Treefern)

Locale: Brisbane
Re: Sources of 1/8" foam on 05/21/2013 03:49:18 MDT Print View

Jeremy, I don't think it's Evazote. But for me I don't think that's a deal breaker. Couple of useful threads:

http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/5464/index.html

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=27718

I also read (but can't find again) a thread in which someone was saying they got a sheet of 3mm EVA foam (not Evazote), but the thickness wasn't uniform. Something to watch out for I guess.

J C
(Joomy) - M
Re: Re: Sources of 1/8" foam on 05/21/2013 05:12:29 MDT Print View

Yes I suppose the difference in R values is not huge, but if I don't get it I'll always want it ;). I might see what this local guy has got in the 3-4mm range and see how that performs as it gets colder.

It definitely seems to be the case that the extra insulation added by thin CCF layers is not as simple at simply adding R-values, so a +/- 10% difference in insulation value probably isn't going to make a noticeable difference, all other factors being equal.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Sources of 1/8" foam on 05/21/2013 05:31:42 MDT Print View

> What's the difference between their EVA30 and the EVA75?
A LOT!
The number is the density of the stuff in kg/cu-m. So EVA30 is 30 kg for 1 cubic metre, while EVA75 is 75 kg. Yep, big difference!

Cheers

Edited by rcaffin on 05/21/2013 05:32:23 MDT.

J C
(Joomy) - M
Re: Re: Re: Re: Sources of 1/8" foam on 05/21/2013 06:39:23 MDT Print View

I guessed that was the case. And I think the Evazote used in GG pads seems to be around 45 or 50. Gives me more info to go looker for similar stuff.

Derrick White
(miku) - MLife

Locale: Newfoundland & Labrador, Canada
Exped UL7 Down v. Synth on 05/21/2013 13:34:54 MDT Print View

I have not used or even handled the syn mat but, based on my experience with the UL7 down mat, I am surprised by peoples' need to use the syn mat with a foam pad to ensure warmth. Based on my experience I would have thought the R value difference between syn and down to be less obvious at those temperatures, i.e above freezing.

These are anecdotal examples but illustrative of the effective R value of the UL7 down mat for me:

1. I have slept in -24C (-11F) on a UL7 LW downmat, inside a 3 season tent (BS Evolution, with only the sylnylon floor between the pad and snow, ie. no foam pad. I wore 2 merino base layers (150 grams each), a toque and fleece neck warmer. I was in a WM Ultralite bag (rated to -7C\20F) covered with EE Revelation 20F (rated -7C\20F), cinched tight and I was toasty warm.

2. Last year while sleeping on a rocky river bed (rounded boulders cemented in place by compact sand) my down mat kept deflating and after pumping it up twice early in the night, and then assuming I had a leak, I managed to find a bearable sleep position and left it deflated and slept on it without air for about 6 hours. The temperature that night got down to -1C (30F). Again, I was toasty warm. Used same bag as above but no quilt.

The next night, the last night of the trip, assuming it had a puncture and because I was sleeping on a sandy beach which was acceptably comfortable, I didn't use my mat and slept with only my sleeping bag (same bag as above) and the silnylon tent floor between me and the ground. That night the temperature went down to 1C (34F) and I was cold the whole damn night, to such a degree that I mummified the bag to the fullest extent possible and maintained a fetal position to stay warm.

Conclusion, the down in the deflated mat provided considerable insulation even without air in the chambers.

Maybe the down mats are a whole lot warmer than the syn mats. I am unsure how R values work. Perhaps the increase in value has exponential effect.

Derrick

John Vance
(Servingko) - F

Locale: Intermountain West
Syn UL7 vs Down UL7 on 05/21/2013 14:52:59 MDT Print View

I have both and experienced feeling a bit cool on the syn mat. I found myself augmenting the mat with a 1/4" ccf pad on most trips and ultimately added the UL downmat.

Down to about freezing I found the syn mat to be adequate if a little cool, but not so much that it interrupted my sleep. With the UL downmat I am toasty but haven't been below 0 f and it is lighter than the ccf and ULSyn combo.

I can't remember the last time I camped out that the night temps were warmer than 50f or so, and as a result I find that the ul downmat isn't too warm and has allowed me to take a lighter bag.

I tried the x therm and the all season but didn't like how narrow they felt but both were plenty warm and packed down smaller than the downmat. If the x therm was a bit wider and not mummy shaped I would most likely have kept it.

J C
(Joomy) - M
Re: Exped UL7 Down v. Synth on 05/21/2013 19:12:48 MDT Print View

"Maybe the down mats are a whole lot warmer than the syn mats. I am unsure how R values work. Perhaps the increase in value has exponential effect."

The downmats are significantly warmer than the synmats, just as a down jacket of a given fill weight is warmer than a synthetic insulated jacket of the same fill weight. As far adding R values goes they do stack linearly, and usable temperature vs. R value also seems to be a linear relationship. I.e. you need roughly the same amount of extra R value to get from 0C to -10C as you do to get from -10C to -20C, etc.

Matt Purnell
(Treefern)

Locale: Brisbane
Re: Sources of 1/8" foam on 05/22/2013 04:15:14 MDT Print View

I went to a craft shop and bought two small sheets of EVA: 2mm x 300mm x 455m (A3; $3) and 3mm x 300mm x 225mm (A4; $2.50). On my scales the A3 sheet weighs 27g, and the A4 sheet 14.5g. According to my calculations that makes the density correspond to something like EVA105 and EVA75, respectively (see for e.g., http://metrofoam.com.au/eva-foam.html).

That's a lot more dense than the EVA30 I think Gossamer Gear is using in their Thinlight pad, but at a couple of bucks I think it's worth a try.

I actually bought two of the A4 sheets, so I'm planning to tape them together and try my mat again by itself, supplemented by the 2mm foam, and supplemented by the 3mm foam.

Any ideas on how to keep the piece of foam centered beneath my hips? Just put it on top of the inflatable pad?

Kate Magill
(lapedestrienne) - F
re: on 05/22/2013 12:48:39 MDT Print View

"Any ideas on how to keep the piece of foam centered beneath my hips?"

Get some McNett SeamGrip or similar. A few stripes on each side of the foam pad should help it stay in place relative to the tent floor and the SynMat.

J C
(Joomy) - M
GG foam on 05/23/2013 03:39:54 MDT Print View

Gossamer Gear's thin light stuff seems to be between 35 and 40 kg/m^3. My local guy (ACT) seems to be able to get EVA in various densities from 30 to 75, in almost any thickness. A two by one by 4mm sheet will cost me 50 bucks. Seems like a good option.

The question is now whether to get EVA30 or EVA45. Thermal conductivity vs. weight vs. density. A denser mat will compress less but a less dense mat has sightly lower thermal conductivity and is lighter.

Edited by Joomy on 05/23/2013 03:51:21 MDT.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: GG foam on 05/23/2013 05:11:41 MDT Print View

> A two by one by 4mm sheet will cost me 50 bucks.
Two furlongs by one furlong for $50 I hope!

A piece 2 m x 1 m x 4 mm should cost but a small fraction of that.

Cheers

J C
(Joomy) - M
Re: Re: GG foam on 05/23/2013 06:11:37 MDT Print View

Well that's for EVA45, the 30 is slightly cheaper. But it doesn't seem too unreasonable considering GG's 1.5*.5*1/8in is 14 dollars.

Phillip Asby
(PGAsby) - M

Locale: North Carolina
dumb question on 05/23/2013 08:01:58 MDT Print View

but the added ccf pad goes under the air mattress? Or on top...

trying to sort out the convective heat loss is coming from the air in the mattress so the ambient air as well as the ground - seems like on top makes the most sense from that perspective but I could rather easily have the theory wrong.

Having said that I have the heavier Synmat 7 (not UL) and it has a good bit higher r rating of 4.9. I was cozy in 22 degrees with my 20 degree down bag and medium weight base layers - a 100g polartec pullover and beanie (I'm bald so a beanie is essential, well, most of the time other than late spring/summer).

Matt Purnell
(Treefern)

Locale: Brisbane
Source of foam and extra foam on top or underneath mat? on 05/23/2013 18:31:43 MDT Print View

@ Jeremy - This company quoted me only $35 including postage for a 2m x 1m x 3mm sheet of EVA30: http://www.kangarubber.com.au/eva.html.

@ Kate - thanks for that.

@ Phillip - I think that's a great question. If it was much of a muchness, then as Kate suggested having the extra foam underneath with some silicon on both sides would seem to have the added benefit of stopping everything moving around.

J C
(Joomy) - M
Re: Source of foam and extra foam on top or underneath mat? on 05/24/2013 00:39:30 MDT Print View

That's cheap, but only about 10 dollar less than the local one. Also this stuff is black rather than blue... dunno if that means there's a difference in quality. Apparently the zotefoams blue foams are less desirable than the evazote black stuff.

As far as under or over the mat. I have heard about people putting the CCF mat over their inflatable mat but that makes no sense to me. It should make at most no difference, I can't see why it would be warmer.

EDIT: Sorry! Got it totally backwards. Meant to say it makes no sense to put the CCF OVER the inflatable mat!

Edited by Joomy on 05/24/2013 02:30:06 MDT.

Matt Purnell
(Treefern)

Locale: Brisbane
Over or under? on 05/24/2013 01:34:20 MDT Print View

"As far as under or over the mat. I have heard about people putting the CCF mat under their inflatable mat but that makes no sense to me. It should make at most no difference, I can't see why it would be warmer."

What have others found? Is under or over warmer?

Dustin Short
(upalachango) - MLife
Re: Over or under? on 05/24/2013 03:47:02 MDT Print View

CCF under is useful for added protection from ground. CCF over has been empirically tested to be warmer. The explanation isn't known but the working theory is that airmats lose more heat to convection and radiation from the tall sides than a CCF. A ccf then provides an initial barrier that reduces the amount of heat lost by these factors. When below you then you have a greater differential in temps within the CCF which increases convective forces along with a greater temp differential along the sides which increases radiative losses. If sleeping pads only lost heat through the vertical axis and conduction then they would be simply additive and it would not matter the orientation. The sides and convection within an air mat do affect the insulation such that order has been shown to matter (to a small degree).

Model it this way, your body is a point source for heat and that heat is lost to exposed surface area of the sleeping pad (like arcs across a semi circle). The air mat has a greater surface area than a ccf. So to maximize insulation (or rather minimize heat loss) you want the item with the least surface area closest to your body. If you did it the other way around, you'd need more CCF to cover all the exposed sides of an air mat (so not just the bottom, but also the sides, like a bathtub) to have equivalent total insulation...which of course is heavier and less efficient.

There's also some potential benefit by having an extra layer of trapped air close to the heat source rather than the heat sink and to also distribute weight more evenly across the top surface minimizing cold spots due to pressure points.

Is any of this particularly noticeable to the sleeper? YMMV... Some even claim that adding a radiative barrier (like foil laminated to bubblewrap products) INSIDE your sleeping bag is warmer than having it between a bag and on top of an air mat, or under the airmat. Similar rationale as above applies with the nuance that reflective barriers work best the closer they are to the initial heat source because there is less matter to transport heat away before the reflective barrier can do it's best work.

Matt Purnell
(Treefern)

Locale: Brisbane
Re: Over or under? on 05/25/2013 01:22:10 MDT Print View

"There's also some potential benefit by having an extra layer of trapped air close to the heat source rather than the heat sink and to also distribute weight more evenly across the top surface minimizing cold spots due to pressure points."

Sort of makes sense if I think of in what order I wear my thermal top, shirt, jumper and rain jacket. I wear it in that order, and that order is warmer than if I did it in any other order. Having the tight fitting thermal next to skin creates a uniform layer of trapped air that's less susceptible to being disturbed than, say, the shirt.

J C
(Joomy) - M
Re: Re: Over or under? on 05/25/2013 05:22:11 MDT Print View

"and to also distribute weight more evenly across the top surface minimizing cold spots due to pressure points"

Doesn't make sense re the Exped mats since the mats would never compress enough to compress the insulation. But your theory about the sides of the mat makes sense. That suggests that letting a quilt drape over the sides of the mat would help increase warmth too.

Stephen M
(stephenm) - MLife

Locale: The Great Lakes Bay Region
Re: Re: Re: Over or under? on 05/25/2013 06:45:10 MDT Print View

If camped on snow amd I put a lot of pressure on one point on the downpad UL (say with an elbow or knee) I can feel the cold coming through if I don't use a ccf underneath.

J C
(Joomy) - M
Re: Re: Re: Re: Over or under? on 05/25/2013 19:20:02 MDT Print View

"If camped on snow amd I put a lot of pressure on one point on the downpad UL (say with an elbow or knee) I can feel the cold coming through if I don't use a ccf underneath."

That makes sense with a Down filled mat since the down fills the entire baffle, so when you compress it it's just like compressing a down jacket - less loft = less warm. But with the Synmats since the insulation is only like 1" thick (or something) and laminated to the inside of the mat, you'd have to compress it a lot to compress the insulation layer.

Edited by Joomy on 05/25/2013 19:24:25 MDT.

Stephen M
(stephenm) - MLife

Locale: The Great Lakes Bay Region
Re: Re: Re: Re: Re: Over or under? on 05/25/2013 20:24:59 MDT Print View

I have never noticed it with the Synmat but have only ever used it well above 0c.

jeffrey armbruster
(book) - M

Locale: Northern California
"Exped Synmat UL 7 felt "cool" under hips at 5-8 deg C" on 05/25/2013 21:53:36 MDT Print View

I just came back from four nights using a Synmat UL7 in temperatures into the mid 20's F with no problems. I blow it up very firm.

I use a Gossamer Gear thin pad--whatever their thinnest is, I forget now--beneath my Synmat more for protection from sharp objects like pine cone prickles than for warmth. Still, this may add a bit of r value.