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What's the benefit of synthetic?
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Jim Colten
(jcolten) - M

Locale: MN
Re: Planned use: Down Sleep system + VB on 09/24/2007 03:09:40 MDT Print View

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

Richard Nelridge
(naturephoto1) - M

Locale: Eastern Pennsylvania
Vapor Barrier Clothing on 09/24/2007 06:41:42 MDT Print View

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:

Here is their pricing page link:


Michael Davis
(mad777) - F

Locale: South Florida
Re: Overbag on 09/24/2007 10:53:37 MDT Print View

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.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Re: Loft Heresey on 09/24/2007 20:00:44 MDT Print View

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.

Harold .
(huppy) - F
equal insulation - down loft vs synthetic loft on 09/24/2007 20:32:30 MDT Print View


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.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: equal insulation - down loft vs synthetic loft on 09/24/2007 23:08:15 MDT Print View

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.

Down Density

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.

Brett .
(Brett1234) - F

Locale: CA
Question on Richards down density graph on 09/25/2007 00:35:23 MDT Print View

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!

Ron D
(dillonr) - MLife

Locale: Colorado
Re: Re: equal insulation - down loft vs synthetic loft on 09/25/2007 06:51:22 MDT Print View

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

Ryan Gardner
(splproductions) - F - M

Locale: Salt Lake City, UT
Like I'm back in school... on 09/25/2007 07:15:58 MDT Print View


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...

Harold .
(huppy) - F
Re: equal insulation - down loft vs synthetic loft on 09/25/2007 08:00:05 MDT Print View


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 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.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Question on Richards down density graph on 09/25/2007 08:21:44 MDT Print View

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.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Re: Re: equal insulation - down loft vs synthetic loft on 09/25/2007 08:40:07 MDT Print View

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.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Re: equal insulation - down loft vs synthetic loft on 09/25/2007 09:05:41 MDT Print View

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")

Home Test

% 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.

Daniel Goldenberg
(DanG) - M
Loft/insulation degradation on 09/25/2007 10:05:45 MDT Print View

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

Harold .
(huppy) - F
Re: Re: Re: equal insulation - down loft vs synthetic loft on 09/25/2007 10:08:31 MDT Print View


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!

Michael Davis
(mad777) - F

Locale: South Florida
Re: Re: Re: Re: equal insulation - down loft vs synthetic loft on 09/25/2007 11:07:25 MDT Print View


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!

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Re: Re: Re: equal insulation - down loft vs synthetic loft on 09/25/2007 15:08:09 MDT Print View

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.

Heat Pad Plot

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.

Plot 3

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

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Loft/insulation degradation on 09/25/2007 15:31:45 MDT Print View

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.

James Schipper
(monospot) - MLife
Re: Loft/insulation degradation on 09/25/2007 16:45:09 MDT Print View

"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.

Harold .
(huppy) - F
Re: Re: Loft/insulation degradation on 09/25/2007 17:38:27 MDT Print View


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.

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?