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

By Damart.

What is that stuff? Do they still sell it?

Hi Justin

> 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.

The process is called shrink-proofing. Yes, well known, since … I dunno, maybe the 70s. It was almost a finished issue when i joined the CSIRO Div'n ot Textile Physics back then. But it does not have much effect on comfort with wool: that is more a function of the fineness of the fibres. Thicker 'coarse wool' fibres stick into your skin a bit more, and feel prickly. Dealing with that probably goes back to the 80s.

> That same smooth fibered wool, still feels a lot warmer while wet than does cotton,
> linen, or rayon.
I would want to see a published reference for that claim – and not some marketing dept spin. It may be true: I think the wool fibres end up smoother and so would hold less water on the surface than cotton. That works when wet.

> then tencel would be more warm when wet than a lot of other textiles, because tencel
> has the interesting property of micro fibrillation,
The 'more warm when wet' bit does not have to be true. Got any published references?

> but when it gets wet, it still cold like cotton, linen, and other rayons.
A fibre with micro-fibrilation on the surface could hold more water than a single plain fibre, as there would be a lot more places for the water to be trapped on the surface. It all depends on the surface tension. I could imagine it being terrible!

Cheers

Interesting stuff David, totally new to me. Found an interesting research type paper on it: http://www.lenzing.com/fileadmin/template/pdf/konzern/lenzinger_berichte/ausgabe_63_1987/LB_1987_10_Menault.pdf

"But it does not have much effect on comfort with wool: that is more a function of the fineness of the fibres. Thicker 'coarse wool' fibres stick into your skin a bit more, and feel prickly. Dealing with that probably goes back to the 80s."

Comfort is affected by both the degree of coarseness or fineness and by the scales from the sources i've read. Fineness will trump scales, but scales are definitely a factor. For example, alpaca fibers are said to be more comfortable at a similar micron count than sheep's wools because the scales are much less pronounced and less numerous on alpaca fibers than sheep fibers.

> That same smooth fibered wool, still feels a lot warmer while wet than does cotton,
> linen, or rayon.
"I would want to see a published reference for that claim – and not some marketing dept spin. It may be true: I think the wool fibres end up smoother and so would hold less water on the surface than cotton. That works when wet."

I'm basing that on personal experience. I've used sport type wools and wool blends and they feel significantly warmer while wet than cotton, linen, and rayon that i've worn while sweating in colder temps.

> then tencel would be more warm when wet than a lot of other textiles, because tencel
> has the interesting property of micro fibrillation,
The 'more warm when wet' bit does not have to be true. Got any published references?"

I'm not saying tencel is warmer while wet, i was using it as a contrast argument. You mentioned the scales of wool trapping more air and thus being warmer, with conductivity having nothing or little to do with it. I pointed out, the micro hairs of tencel would do similar, and yet in my experience, tencel while it can feel warm when dry, does not compare to wool with scales or wool without scales in comfort and perceived warmth when all are wet. The point being is that conduction level of the material itself may play as a factor. Check out that recent Lenzing paper i linked, it talks about the importance of conductivity of the material itself in comfort and perceived and actual warmth of a garment some;

> but when it gets wet, it still cold like cotton, linen, and other rayons.
"A fibre with micro-fibrilation on the surface could hold more water than a single plain fibre, as there would be a lot more places for the water to be trapped on the surface. It all depends on the surface tension. I could imagine it being terrible!"

That "COULD" be the case, however, it's not germane to the core debate to begin with. I don't think tencel makes a good cool to cold weather textile for active conditions. However, in my subjective experience, though tencel absorbs more moisture than cotton, it seems to release moisture faster than same. I don't know if my tencel garments though, have that micro fibrillation affect going on. They may not. It is said to be a common innate trait of that fiber though, but it can be manipulated in different ways.

Hi Justin

> Comfort is affected by both the degree of coarseness or fineness and by the scales
> from the sources i've read. Fineness will trump scales, but scales are definitely
> a factor.

Hum – I spent 27 years in textile research, and I don't remember ever meeting the claim about scales directly affecting comfort. Coarse guard hairs in the wool will absolutely kill the comfort, but Merino has very few of them. The primary follicles have been reduced in both % and fibre diameter relative to the secondary follicles – by a lot of breeding.

Alpacas – not sure. I was handling some alpaca wool straight off the animal last weekend, and it seemed less stiff to me, but I would want to actually MEASURE the stiffness before going any further.

Cheers

I did some quick research Roger regarding this issue. Here is an Argentinian research paper, which is addressing comfort factors of wool–particularly in connection to Llama wool. However, they address other wools includings sheep, and talk about some similar generalities and differences.

http://www.ijastnet.com/journals/Vol_4_No_3_May_2014/7.pdf

See especially the 2nd page, 2nd paragraph on said page–i will quote from same, "This can also be demonstrated with some other external characteristics of the fibre such as
cuticle scale morphology and/or attributes measured as a scale index (Singh Mahal et al., 1951). Hausman (1920) found that the cuticle scales varied according to the cross section of the fibre, and that the cross section is closely related to the medulla/fibre type (Villarroel, 1959; Frank et al., 2007). ****Also, when fabrics were treated with **silicones, the fibre/fibre friction effect was diminished with an important concomitant prickle reduction** (Naylor et al., 1992). It is evident that the effect of the silicone treatment changed the cuticle scales characteristics.****"

**** and ** my emphasis.

Translated for the layperson who may be reading; Researchers noticed that when they put a silicone coating on the wool fibers, which filled in the scales with silicone, the prickle/discomfort factor lowered.

Seems i'm not the only one who thinks that scale attributes can affect the degree or lack of comfort. However, as the paper above addresses, it is primarily the diameter of the fibers which most contribute to these factors.

I may not have a couple plus decades of research in textiles, heck, i'm an unedumacated nobody without a college degree of any kind, but i do have a decent memory for things i'm more intensely interested in (and i'm VERY interested in textiles/fibers), as well as an innate sense of and capacity to apply holistic logic (aka, a developed perceptual acuity and broadness).

Looking at especially sheep wool fibers under a microscope, or in my case, pictures taken under those conditions, it just makes sense that the nature of the scales would probably contribute to factors related to comfort or a lack, and taking off or filling in the scales as is a common practice nowadays, will tend to increase comfort to a measurable degree, though not more important than the overall size of said fibers.

Or to put it another way, a garment made out of wool fibers including scales with an average micron count range of 25 to 28 microns, compared to a garment made out of wool fibers sans scales but also with the average micron count range of 25 to 28 microns–well the latter should by both holistically applied logic and research feel a bit softer and less "prickly".

Anyways, we have digressed far off the original intention and premise of this thread–the fabulous and more truly "warm while wet" properties of kevlar fabric due to it's super low conductivity for a solid material.

I should have known, if something sounds to good to be true, it most likely is. I had a nagging feeling that i should do more research into kevlar and it's properties.

I found this research paper:
http://jpkc.dhu.edu.cn/gjsxw/COLUMN_7/file_1.files/
Thermal%20conductivity%20of%20Kevlar%2049%20between%207%20and%20290%20K.pdf

"It is worth noting that, because of an original misprint in the
Kevlar technical guide [15], the exotic value kKev ¼ 0:04 W=mK is
often reported for the room temperature thermal conductivity of
Kevlar 49 [16]. This value is very close to that of air,
kAirðSTPÞ ¼ 0:045 Wm1 K1"

Then i found this from another web page:
http://mtm-inc.com/reduce_project_risk/kevlar_supports_for_cryogenic_vessels/

"The high strength and relatively low thermal conductivity of Kevlar (0.14W/mK at 100K) make it an interesting choice for thermal supports in cryogenic vessels, particularly in applications in which a very low heat leak and/or low weight are required. "

Strange that the top listed google, DuPont pdf data pages still contain this error! You would think that they would have fixed this egregious mistake by now.

So, kevlar is a pretty low conductive material for a textile, but no where near the listed misprint level. I did somewhat question how a solid could come close to a gas in conduction, but i naively trusted in DuPont's listed data and thought it's unusual other properties may some how have contributed.

I apologize for putting out this erroneous info and possibly getting some high hopes up. It still would make a good cool to cold weather, warmish while wet fabric, but not the unusually excellent one that it first appeared.

Didn't wade through some long comments on this thread, but would this play a role here?
When you touch a cold material (loose garment that was few seconds away from your skin and cooled down, a sleeping pad when you roll over, plastic toilet seat vs wooden toilet seat) your skin just needs to warm the surface of the material to feel ok. That is easier if said material has low conductivity and low heat capacity. Tight weave Kevlar with not much place for water could feel nice to touch even if not thick enough to insulate well?

Then if you'd coat Kevlar with silicone to improve water repellency, would it be better?
Like this: http://www.extremtextil.de/catalog/100-Kevlar-coated-anthracite::394.html

Hi Alpo, that essentially was the premise of this entire thread.

However, i just found out that DuPont's listed conductivity of Kevlar 49 at .04 was a misprint!

It should be .14, which is a significant difference, though you could still call it a low conductive material.

Some have reported that thin, tightly woven nylon fabrics tend to feel more clammy and cool on bare skin than thin, tightly woven polyester fabrics. This may be due to the difference in conductivity with polyester being less conductive than nylon.

An interesting hypothetical situation to test, would be something like this. Imagine a tightly woven, all dyneema fabric that you use for the shell and liner to make a highly lofted, high quality goose down quilt or bag. The down would provide plenty of insulation, but the highly conductive nature of the dyneema, well in scenarios as you mentioned, as soon as the dyneema fabric gets separated from your skin, it would rapidly cool and then feel cool to the touch.

Despite the fact that you are still getting tons of insulation, perceived warmth might go down, in other words it likely would feel less warm and comfortable than a fabric with a much lower thermal conductivity.

This is assuming bare skin. Many don't sleep nekked in colder weather out in the wilderness.