A new look at Kevlar textiles and fabric in terms of insulation, particularly for gloves and socks

However, the conductivity of the Kevlar fibres is almost irrelevant to the thermal insulation of the fabric: the fibres would be very thin and very long. They can be ignored. It's mostly about air movement with the fabric.

Cheers

Based on experience, i'm not sure i fully agree. Some fabrics definitely feel warmer while wet than others. Cotton, linen, the various rayon's, etc feel pretty cold while wet, and nylon feels a bit cool when wet. Wool, polyester, and polypropylene feel warmer while wet, and kevlar feels the warmest while wet that i've tried.

The only thing that can explain that, is the relative difference in conductivity of the materials involved. I didn't know about thermal conductivity of kevlar when i noticed this during use.

I would agree that in dry fabrics, the conductivity of the material itself is not that important as is the amount of air it traps/stills. There are probably fabrics out there that are warmer while dry than kevlar because of the size and structure of the fibers. Ultra thin/fine fibers, crimped fibers, fibers with scales, thin but hollow fibers, trilobal shaped etc, etc can and will still more air than round and larger fibers.

So an ideal use for kevlar fibers in this area, would be thicker but flatter fibers that are densely woven in combo with thin, fine fibers that are less densely woven as a top layer. When wet, the former help, and when dry the latter help in insulation. Have the flatter and thicker fibers closest to the skin and the layer of thinner fibers above same–ideally in a lofted way like Polartec Thermal Pro or Pile. Or again, make a grid fleece out of it if it's possible.

I'm not sure if kevlar can be manipulated in these ways though. Any insight into this aspect?

The fire resistance waffle weave nomex long johns for military pilots can be found. It is a similar aramid fiber.

Maybe you could try them out?

http://www.ebay.com/bhp/nomex-underwear

Hi Justin

> Some fabrics definitely feel warmer while wet than others.
Very good point, and one which has not been much explored. It's a bit technical. My thoughts (based on many years of textile science) are as follows, but I have to add that I don't have any published references right now.

When a fabric gets wet the water is 'inside' it. Let's give it a shake and a squeeze, to get rid of the excess bulk water. What's left? There are two places for water to remain: as a thin film on the surface of the fibres, and as micro-drops at the cross-overs, where fibres are touching. This remaining water will very seriously alter the thermal conductivity of the fabric by altering any heat flow through the fabric, by evaporation and diffusion. The more water there is, the more evaporation and diffusion inside the fabric, and the poorer the insulation.

Now, how can you alter the amount of water left in the fabric? By altering the surface tension of the fibre material. Natural fibres tend to 'attract' water so it sits on the surface of the fibres, 'wetting' the fibre. Cotton and de-oiled linen are very good at doing this, which is why we make towels out of them. Synthetics are not normally good at this: the water does not wet the surface. So by shaking a synthetic fleece out you get rid of far more water than you would with a cotton tracksuit top. The cotton stays a whole lot 'wetter'.

Result: the synthetic fleece restores its insulation value much faster, and feels warmer.

HTH
Cheers

Roger's comment about shaking garments reminds me of a recent article about dogs shaking water from their fur. Sorry I don't have a link but the point was that it is a very effective behavior. A large % of the water is removed by those energetic shakes.

I've got insulation wet, weighed it, calculated percent of volume that's water (which is very small), calculated over-all conduction using conductivity of water and air – the higher conductivity of water has very little effect on the over-all conductivity – too lazy to find my calculations

I think that it's almost totally evaporation – if the fabric gets wet, and then body heat evaporates it, that makes you colder.

So, the less water the fabric absorbs, the better.

Cotton absorbs more water so it's worst. Wool better. Fleece good. Nylon and polyester good.

Jerry, I've found the same thing with evaporation causing the most heat loss. If I put on a windshirt to slow evaporation or a rain jacket to cutt off evaporation completely, then I feel so much warmer.

Thank you David, i'll have to check into the specific properties of Nomex, but it may be worth a try.

"So, the less water the fabric absorbs, the better.

Cotton absorbs more water so it's worst. Wool better. Fleece good. Nylon and polyester good."

Yes, this above part is obvious, and yet, as Roger has often pointed out, sheep's wool is one of the worst offenders in absorbing moisture. Sure, it can absorb a lot into it's interior before it feels wet, but it's way worse than cotton for total moisture regain, and yet, it feels significantly warmer than cotton even when both are sopping wet.

Take linen. Linen has a similar property to wool (though not to the same extreme degree), in that it can absorb a good amount of moisture before it feels noticeably wet, but as soon as it's damp, it's very cool feeling. (this is because it's fibers are hollow, absorbent straws essentially, a lot of moisture can go into the interior). It's conductivity though, is much more similar to cotton than to wool, despite the other similarity…

It seems that the conductivity of the fabric material itself may be in play here.

Take Kevlar. Kevlar 29 has a moisture regain of 7%. This is fairly high for a synthetic material. It's close to cotton, and yet my experience is that it feels pretty warm when wet.

Something else seems to be going on here. Edited: see last post by me, DuPont had a misprint on their conductivity data. It is still listed as .04 for Kevlar 49, but should be .14.

I think the conductivity of air is what's important.

The conductivity of the fiber material is not important, because most of the volume of insulation is air. More thinking of synthetic or down insulation than wool or fleece, but I think they're probably the same.

My question is, if the fabric doesn't absorb the water, where does it go?

If it's rain, maybe it goes to the ground.

For sweat, you want to minimize sweat by not wearing too much.

"Jerry, I've found the same thing with evaporation causing the most heat loss. If I put on a windshirt to slow evaporation or a rain jacket to cutt off evaporation completely, then I feel so much warmer."

In a round about way, you've indirectly reminded me about another point related to this whole issue.

Quick evaporation (low moisture regain and well wicking synthetics) can be bad and can be good depending on the conditions. I've experienced the flash dry cold effect at very cold and drier temps, it's not fun, especially with wind involved.

Yet wool, which absorbs a lot of moisture, felt more comfortable in these same conditions. It seemed to slow down and make the evaporation process more steady/consistent.

Besides the super low thermal conductivity, at least one type of Kevlar can absorb a fair amount of moisture itself for a synthetic. Perhaps this also contributed to the perceived warmth, because the evaporation process wasn't happening so quickly/efficiently, that and it wasn't a "wicking" type material?

Either way, whatever the actual reasons and logic behind it, i've observed from experience that Kevlar seems to be a particularly good fabric for cold weather activity because when it gets wet, it seems to retain more warmth. There could be various factors for this, but to argue that the super low thermal conductivity isn't meaningful in any significant way, doesn't seem to fully fit a holistic look at a wide range of fabrics with a wide range of thermal conductivity levels and moisture regains. Wool, low conductivity, super high moisture regain yet warm when wet. Cotton, moderately high moisture regain, yet cold when wet, Kevlar, super low thermal conductivity for a solid, moderate moisture regain, yet quite warm when wet, etc, etc.

Again, i don't exactly why it (Kevlar) works so well, but it works. We could talk theory and logistics all day, and yet at the end of the day experience is the proof in the pudding, if something works, it works, and no way to know for sure, unless you try it out yourself. The only references i've ever seen to kevlar being used as a thermal insulation fabric for hiking on BPL, are my own past mentions. Hence, it doesn't seem that too many have much experience with using it in this manner.

> sheep's wool is one of the worst offenders in absorbing moisture. Sure, it can absorb
> a lot into it's interior before it feels wet, but it's way worse than cotton for
> total moisture regain, and yet, it feels significantly warmer than cotton even when
> both are sopping wet.

There is a reason for this. Most natural fibres are smooth, but wool fibres have scales. (The scales are why wool felts up so badly.) Provided it is not masked by surface water, each scale edge captures far more boundary layer of air than the smooth surface of cotton. That makes the wool a much better insulator than cotton.

But, your body is still losing a lot of energy evaporating all that absorbed water off.

Cheers

So I did some possibly relevant research some time back, to understand why Orlon socks felt drier than cotton or wool for pro athletes. The bottom line is that the modulus of natural fibers drops dramatically when wet while synthetics stay about the same. Basically the open fabric structure collapses especially cotton. The same may be happening with the clothing that is perceived as being colder when wet.

Kevlar(r) also has an additional interesting property, it has a negative coefficient of moisture expansion, thus the filaments shrink slightly when wet. This can bulk some fabrics.

Cliff

"I think the conductivity of air is what's important."

Mostly, especially when dry. Less so when wet, because the air gets displaced by moisture in the form of both liquid water and water vapor, both which are much more conductive than air.

"The conductivity of the fiber material is not important, because most of the volume of insulation is air. More thinking of synthetic or down insulation than wool or fleece, but I think they're probably the same."

I'm talking more like baselayers, liners, etc. Yeah, air volumes wins out a bit here, but if you have a solid fabric that starts to approach the non conductivity of air, and the water displaces the insulating air because it gets wet… wouldn't it make sense then to have a material that is unusually non conductive in that situation?

"For sweat, you want to minimize sweat by not wearing too much"

I agree, but this is way easier said than done. You can get wet by sweat, wet from rain, from snow, etc. It's very hard to be very active and not sweat or get wet to an appreciable amount at times. This is why the Inuit and Native Canadians and Alaskans tend to move kind of the slower but steady side most of the time, as not to sweat too much. We sweaty backpackers are a different breed, dealing with different conditions and expectations. We don't need to avoid sweating to the degree that they do, nor are we willing to limit ourselves to that degree to avoid same.

Meanwhile, wouldn't it make sense to wear fabrics that do remain more truly warm when wet during colder conditions? Isn't this why everyone says to avoid cotton in winter?!? Isn't that same cotton nice in the desert during summer? I'm just looking at this from a different, but related perspective…

"There is a reason for this. Most natural fibres are smooth, but wool fibres have scales. (The scales are why wool felts up so badly.) Provided it is not masked by surface water, each scale edge captures far more boundary layer of air than the smooth surface of cotton. That makes the wool a much better insulator than cotton.

But, your body is still losing a lot of energy evaporating all that absorbed water off."

Ah, but Au contraire, mon frère, most sport wool company's and fabrics today, treat the wool to either take off the scales or fill them in with a polymer. In either case, it's to increase the comfort level of the wool and to avoid that same felting and shrinking issue so prevalent in sheeps wool.

That same smooth fibered wool, still feels a lot warmer while wet than does cotton, linen, or rayon.

Besides, if this was solely the case for this, then tencel would be more warm when wet than a lot of other textiles, because tencel has the interesting property of micro fibrillation, wherein when it gets wet or if it's designed in a certain way, it has like micro hairs (sub fibers) that branch off the main part of the fiber. This, theoretically can still more air. In a sense, it's a minor similarity to down.

Yet, while it can actually feel fairly warm when dry, but when it gets wet, it still cold like cotton, linen, and other rayons. Again, this may be due more to the fact that cellulose is a good thermal conductor, particularly when wet.

Look, having been "schooled" by you and Jerry before, i've learned to think things through more deeply and holistically before posting this kind of stuff. You guys have kept me on my toes, and now i try to not overlook important variables and/or do more research before hand.

Good points Cliff, probably definitely a contributing factor. Interesting about kevlar slightly shrinking when wet.

I don't know how much nylon does or doesn't swell with moisture when wet, but i've noticed that nylon is kind of in between the cellulose type fabrics and most of the other synthetic fabrics in it's level of warmth while wet properties. It's not freezing cold like cotton, etc, but neither is it particularly like polyester, polypropylene, nor animal protein based fabrics like wool.

I would imagine that Wool fibers tend to swell with increase moisture absorption, probably more than nylon?

No one has yet convinced me that thermal conductivity plays an insignificant part in at least "perceived" warmth while wet.

seperate subject – when my wool socks get wet they're a lot more susceptible to wear. I can wear out some socks in one day. Maybe some are worse?

All sheep's wool loses significant amount of tensile strength while wet. This is why it's important to go for the higher quality stuff wherein they twist the fibers more and more tightly (packing more individual ones in a smaller space) to increase the overall strength of the yarn–another example of strength in numbers/unity concept.

Darn Tough Socks seem to have very high quality, very well spun and twisted yarns, which they then expertly knit for maximum durability. I would argue that putting in at the very least 15% nylon content also helps, and the more the better.

Or…use cheaper wool socks, but avoid sweating so much ;)

"stuff wherein they twist the fibers more and more tightly"

The common term for that is worsted wool.

–B.G.–

Yep. Describing the process/reasons in general terms seemed more apropos.

" So, the less water the fabric absorbs, the better. "

so yes, sure. but there seems to be more in play here than simple intuition is going to get us thru.

one can put on a marmot precip jacket over bare skin or a T shirt and feel warmer.
but, if i do that with my packlite parka, the effect feels cooler.

neither fabric really soaks it up like one of the baby diapers on tv that blot up blue pee like a vacuum cleaner
and for a fact .. NEITHER will swell to bursting a glass of water like a television tampon.
they are both very much just plastic. yet one feels warmer than the other.

there must be factors at work we are not party to beyond half a bottle of wine.

v.

Indeedily, you got to know all the variables before quantifying something more accurately.

I'm going to use another fabric as an example, that in some ways is the opposite of, and yet in other ways similar to Kevlar.

Dyneema. Dyneema is on the opposite spectrum of Kevlar in conductivity. It's the most conductive material that i know of, that is used for fabric. Unlike Kevlar though, it absorbs almost no moisture–in this sense it's like polypropylene.

I have some protective dyneema sleeves that i've used for motorcycle riding. This fabric feels amazingly cool on my body. This seems to be because of two reasons, one, the fabric material itself is extremely conductive and two, it doesn't trap a lot of air. It doesn't trap a lot of air, because the fibers (yarns?) are large, smooth, and round.

Despite the fact that it absorbs almost no moisture into the material itself, i imagine that it would be even worse for a baselayer than cotton for cold winter temps, unless you make it into a fishnet type baselayer.

Now, it might have a future if you could make it wicking and add odor resistance, for very hot and very humid weather garments.

My bet is on two bottles of wine and a six pack. That will reveal any truth one can think of.

We can't handle the truth!