Synthetics: Just HOW warm when wet?

“Another Viewpoint” But…
one which is very much a MINORITY view and contradicted by the overwhelming number of folks who participate in outdoor activities. The almost universally accepted adage is that “Cotton kills…” (when it’s wet and cold out).


Running = different requirements
…from paddling.

With paddling, not only is your front door far away, there is always the chance of getting soaked from either spray or immersion, not just sweat. Doing a routine run near your home is a much different case from camping paddle trips, where many variables can prevent changing quickly into dry clothes.

If you had to stand outside for 2 hours AFTER a sweaty run, without changing into a dry set, how would you feel?

Cotton insulates only when it’s dry. That part is the same regardless of sport. If your sweat evaporates at just the right rate, you’re OK. But there isn’t much margin of error. I’ve worn a thick cotton sweatshirt as outermost layer (synthetic base layers) for winter cycling (20 deg. and extremely dry air) but it’d be a hazard to paddle in because it soaks up moisture like a sponge and is very slow to dry.

Answers to your questions and more

Q - Synthetics are supposed to be much warmer than cotton when wet, but just HOW warm?

A – Synthetics will be up to 25 times warmer after a few seconds to expel the accumulated moisture between the fibers through shaking or wringing.

Q - If caught in rain or otherwise damp, on a multi-day trip, would I still be comfortably warm, or is it just a RELATIVE thing (wet and cold, but not AS cold?).

A - Yes you would be comfortably warm.

Q - Would I still need several changes of clothing, or could I cut back? What has been your experience on multi-day trips?

A - One change of clothing (similar to what you received at Christmas); one synthetic insulating sweater plus vest with a combined loft (thickness) appropriate for the lowest temp and activity level planned; and a waterproof/breathable shell is all that is required for a trip of any duration kayaking trip in rainy / cold weather.



When you are sleeping you only generate about 70 watts of heat. This is why your sleeping bag must be much thicker than the clothes that you wear during the day. When are seated just watching the river go by you are generating about 115 watts of heat. When you are doing light work such as easy paddling you are generating about 150 watts of heat. When you are doing medium work such as chopping firewood you are generating about 265 watts of heat. When you are doing heavy work such as carrying your kayak up a steep hill you are generating about 440 watts of heat. This variable heat generation is the reason that it is necessary to layer clothing so the insulation prevents a heat loss greater than what you are generating. Four layers of clothing can be removed and added as is required for the temperature and activity level. If you have too many clothes on and start to sweat, the air cells in your insulation will be displaced with water and your insulation value will be lost just the same as if you capsized or got rained on.

THICKNESS EQUALS INSULATION WARMTH Trapped air in your clothing is what keeps you warm and not the actual material itself. One inch of cotton, fleece, Primaloft, Polarguard, down, or even steel wool would provide roughly equivalent insulation when dry. Multiple layers of loosely fitting clothing best achieve insulation thickness because up to 12 mm of space between two clothing layers serve as additional insulation. When exposed to moisture the natural fibers displace the air in the fibers with water it and it takes the natural fibers a very long time to dry.


It takes three minutes to die without air. It takes three hours to die if your core body temperature drops five degrees. It takes three days to die of dehydration. It takes 3 weeks to die of starvation.


Since you paddle in the Detroit area you could choose to go paddling in extremely cold weather. Start with the insulation thickness you need for your sleeping bag. Your clothing loft (thickness) requirements can be derived from that. For 60F your sleeping bag top loft thickness should be a min of .75”. For every 20 degree drop in the lowest temperature you expect, the required sleeping bag loft goes up .5”. For light work, your clothing insulation value should be ½ of what you need for sleeping because you are generating more metabolic heat. For medium work again reduce it in half. For heavy work reduce it in half one last time. The head and neck are highly vascular and this area also needs to be covered by an insulation thickness comparable to the torso calculations above.

A fleece jacket and vest combination can be acquired very cheaply and will provide a maximum combined insulation thickness of about .5” (Polartec 300). If you need thicker insulation then that a high loft Primaloft or Polarguard sweater will provide up to additional 1” insulation. A good example of this type of insulation is the older style Wild Things hooded sweaters and vest. They provide 1” of insulation via two layers of Primaloft 1 and can still be found on closeouts for about $100 each.


If the trapped air in your clothing is replaced with trapped water, your insulation is lost regardless of the insulation type. The fibers in synthetic insulation don’t absorb water. The water between the fibers, in synthetic insulations, can be thoroughly expelled by either ringing them our or vigorously shaking them. The fibers of cotton, and to a lesser degree, those made of wool or silk absorb water and can’t be thoroughly expelled by shaking or wring.

If your rain suit is not breathable and you are active, then your perspiration will wet your insulation from the inside the same as rain would from the outside. Breathable rainwear alternatives based on my experience are listed from the best to the worst: eVENT, Propore (Rainshield 02), Pertex Microlight, Pertex Epic, Gore-Tex Paclite, Gore-Tex XCR, 2 Layer Polyurethane such as Marmot’s Precip, and silnylon (nonbreathable). As an example, a high quality Lowe Alpine Elite mountaineering jacket using eVENT can be purchased for about $200 on sale. At the other end of the breathability scale the Marmot Precip jackets can be found on sale for about $70.


In your post you said that have a rain suit. This will solve the problem of forced convection (wind) protection. If it is not breathable and you are active then you need a breathable outer layer. The cheapest solution is an uncoated windbreaker for wind protection and your rain suit for rain if it is not breathable and you are not active.


If your total insulation is greater than ¾ to 1” then radiation losses from your body will be eliminated. The fibers in the insulation absorb the radiation and keep the insulation warm. Foil barriers such as Space Blankets primary benefit is blocking infrared radiation in cases in which you don’t have adequate bulk insulation or to reflect the campfire to your back.


Purchase one additional set of poly underclothing if you like the pair you received at Christmas. Purchase either a fleece or high loft synthetic sweater/vest combination depending on the total loft required for the temps you will be kayaking in. Replace or augment your rain suit if it is not breathable. Use a compression sack for all of your high loft clothing (other than Primaloft and Polarguard) to dramatically reduce the packed size. Primaloft and to a lesser degree Polarguard will permanently loose their loft if tightly compressed.

Minor additions to my earlier post
First, no waterproof breathable rainwear, including eVENT, will prevent sweat from dampening your insulation layers if you are doing heavy work. You need to augment the breathability by venting the jacket. Features such as pit zips, core vents, and 2 way zippers are a mandatory requirement for effective venting.

Second, you need to have equilibrium between the heat generated and heat dissipated. Layering and venting to feel just very slightly cool be best achieving this goal.

Over here, “acryl” is not used much
and I am not sure what it means. It could be another variant in the polyester-Dacron spectrum. Some of our puffy, soft polyesters behave as you describe for acryl.

Got that right
when doing winter climbing it’s heat management. too much venting will keep you too cool and there’s only som much food in the pack. Between climbing or snoeshoing and keeping warm your’s already eating a lot.

Different weaves of the same type of material can have vastly different characteristics when wet. My textured thermax gloves weigh five times what my silky capilene ones do and if they get wet that weave traps moisture. The thermax is much warmer when dry, much less warm when wet, both are synthetic.

Excellent Note by Richard295!
The human heat production Richard listed in his post are hard to find, and rarely make print. That, plus the insulation required relative to the heat output and moisture impregnated insulation, provides rare info worth saving. Thanks!

aye carumba
was that an intense posting… i’m whipped just reading it.

Not true

– Last Updated: Feb-23-05 1:24 AM EST –

The big difference between synthetics and cotton is that synthetic fibers (polyester or polypropylene) do not absorb significant amounts of moisture (typically less than 3%), whereas cotton soaks up water like a sponge. You can dunk a fleece shirt, wring it or shake out the water, put it on and it's warm immediately, since once the moisture is removed, the loft is restored. Try that with a cotton sweatshirt and you'll have a wet mess with no insulating value stuck to your skin and be cold and clammy for hours.

I often wear fleece hats while paddling in the winter and they occasionally get soaked. All I have to do is shake out the water and put the hat back on, and I'm warm.

I also wear fleece garments under my dry suit. They never get soaked, but the do get damp with perspiration during heavy exertion. They'll also dry out if I reduce my effort level and stop sweating. If I was wearing cotton, it would get soaked and stay that way.

Very interesting post Richard295 !

and I have also experienced that insulation of different materials

varies under different circumstances. From my experiences with all

kinds of socks (in open sandals) I have found that compared to

cotton, acryl or polyester fleece, wool is the warmest when wet and

windy (although still not as warm as needed sometimes…) Cotton is

really cold. Acryl socks are reasonable warm when dry and no wind,

but suffers much when wet. Polyester fleece does last longer than

wool and acryl (socks), but is relatively colder when wet and windy

(and really smells…).

Also I have experienced that polyester fleece clothing needs a good

windbreaker on top, otherwise it looses relatively too much of its

insulation. Except perhaps Polartec WindPro, that is rarely used in

fleece clothing nowadays? (I wonder why?). Wool seems much better in

that respect, in my experience. If it was not for the high cost,

very long drying time, heavier weight (especially when wet),

difficult laundering and possible lower durability and

uncomfortable wearing on the skin, wool would be my choice for

all outdoor clothing. Now my preference for underwear in varying

paddling conditions, is polyamide (Tactel) boxers (because it feels

softer in the long run, so it seems) and polyester Trevira 350 or

similar) shirts and long trousers. Warmer than cotton in most

cold+wet situations, and cool enough in hot situations, and durable

enough for its price. But I am now preparing for a trip in much

(longer) colder conditions, and am considering to add wool or acryl

for that, but I have my doubts if wool is worth the money and acryl

performs well enough as underwear when wet.


– Last Updated: Feb-23-05 10:48 AM EST –

You have received a lot of good info. There can be a lot of talk about degrees of warmth and such, but the bottom line is when it comes to water and cold; COTTON KILLS !!!

COTTON KILLS, and I have never heard anyone state otherwise, or argue against the statement.

Do I wear cotton on cold water? Shhhhh ... don't tell anyone I do, but I also do it with full knowledge of the risks I take. I also have cut through the ice almost every spring and gone swimming too so I have experience and know full well the risks I'm taking.

I used to day paddled with Verlen Kruger on "his" river down to 10*f and he wore cotton jeans every time, but did so knowing full well the risks and took into account the environment he was in. We both knew if dumped we only had minutes to abandon the equipment, get out of the water, and keep moving or face death. To him facing cold wet cotton on his home river was minor compared to his experiences and skills from his 100,000 miles of paddling everything. You have to judge how your knowledge and skills compare to the environment you put yourself into.

Do not go overboard and spend too much too quickly either. Shop the sales. Buy in discount stores. Build up your non-cotton stock of clothing. Use cotton with knowledge and respect for the power of hypothermia!

To answer your question of how warm are synthetics? All synthetics (and wool) are a heck of a lot warmer than the warmest cotton when wet!!!

And always remember COTTON KILLS !!!

Happy Paddl'n!



Acrylic is cheaper but not durable

– Last Updated: Feb-23-05 12:53 PM EST –

I haven't used acrylic long underwear but that's been my experience with socks, hats, and sweaters. It just doesn't last as long as other synthetics, let alone wool.

It works up one h3ll of a static charge, too.

Last but not least, it really STINKS up badly with even a little sweat. As bad as the original-generation of polypropylene.