Monday, December 3, 2012

The Best Material For Winter Clothing - Staying Warm When Wet… and Other Fairy Tales

So, winter is around the corner. That means that the talk of magical materials has begun. As fashion has had it in the past few years, there have already been several posts about the magical properties of wool, and how it keeps you warm when wet. Apparently the myth has now grown to include other properties such as durability, toughness and light weight, things which are pretty squarely in the realm of imagination. Wool of course is not the only offender. Many other posts have come out talking about newer materials which perform equally magical feats of insulation.

I am writing this post in an attempt to give you my view on all of this hoopla, and if possible share with you my experience, both practical and academic regarding the insulation abilities of different types of clothing.


I will start by summarizing my views on all this, and say that there is no fabric, (short of a fully waterproof material like closed cell foam) that will keep you warm when wet. Not wool, not fleece, not any material currently available or likely to be available. Some fabrics provide a bit more insulation than other when wet, but the difference is marginal. At the end of the day, wet is wet; and wet is cold. I am not sure what support is being offered for claims about certain materials retaining as much as 80% of their insulating ability when wet, but despite all my searching, I have not been able to locate any such studies.

I first became skeptical of all these claims last year. For many months prior to that point I had been reading on all the forums about the magical properties of wool, and how it did not matter if it got wet because it would still keep you warm. People were going as far as using it as rain wear because it didn’t matter if it got wet. So, I tried wearing wool clothing all year long. It quickly became apparent that those claims were no more than old wives' tales. I could immediately feel that any part of my wool clothing that got wet, got much, much colder than the dry clothing.

So one day, I did an experiment. I put a heat source in a dry wool cap and measured the heat loss. I then wet the wool cap and repeated the experiment. I repeated it both with the wool cap being wet only initially, and then with continuously making it wet. The results clearly showed that the wet wool provided significantly less insulation than the dry wool. You can see the results here.

I then repeated the test with merino wool, fleece and cotton insulation. All of the fabrics failed to maintain their insulation when wet. While dry wool provides good insulation, wet wool provides less insulation than if you were wearing no clothing, but were dry. Similar results could be seen with the other materials.

The reality is simple. If you want to stay warm, you have to stay dry. If you plan on being wet, you need a completely different type of clothing that is completely waterproof like a dive suit. Any fabric that absorbs water will lose significant insulation. If you are wearing sufficient clothing to be thermally neutral (you are not cold or overheating), once that clothing gets wet, you will be in trouble. 

My view on this issue was confirmed by an article I found recently published in 1989 by the Canadian National Defense, titled Some Practical Advice on Cold Weather Clothing:

In the article the author states that the insulation properties of the fabric from which the clothing is made is not the important part with respect to whether the clothing will keep you warm. The important factors according to the article are the thickness of the insulation, the dryness, the wind proofness, whole body coverage, and flexibility. The article was written by the Canadian National Defense (according to the writer) to provide to the general public the knowledge that has been acquired by the military from prolonged (multi day) stays outdoors in cold temperatures. Here are some abstracts:

“I am frequently asked “What is the best insulation for winter clothing?” It is inspired by the belief that the best clothing is automatically that made from the best material. There is a widespread belief in what I call “Material Magic”. The disappointing answer is that it doesn’t matter very much what clothing is made of. How it is made is much more important. Good design, not magic materials, are the key to good clothing.”

“The old mythology of clothing said that for warmth-when-wet, it had to be wool. The modern mythology says that synthetics such as polyester and polypropylene are warm when wet. So will the real magic material please stand up! Both myths are precisely that. Any material which is wet is no longer an insulating material.” 

So, now what? Well, after struggling with clothing that was supposed to keep me warm when wet, and didn’t, I decided to change my approach. I have focused on two things. The first is staying dry, and the second is drying out quickly when I do get wet.

For the first part, I have invested in well designed rain gear and snow protection. This time I have decided to avoid making a decision based on claims of magical fabric performance. All sorts of absurd claims have been made about fabrics from Ventile to eVent about how they will keep you completely dry while at the same time being as breathable as a cotton t-shirt. As you may expect, those claims are as true as those about magical fabrics keeping you warm when wet. The truth is that while some materials are more breathable than others, they are pretty much as breathable as a plastic bag when they get wet. For me the design of the clothing is much more important. It has to be light enough so that I can always carry it with me. It has to be compact for the exact same reason. I will not be backpacking while wearing a Ventile or Gore Tex coat, no matter how breathable it claims to be. It goes in the backpack until I need it. Once I do need it, it has to fit well and be easy to put on. As an example, I’ve invested in rain pants with full side zips. I know from experience that I will not stop to remove my shoes once it starts raining.

As far as the second part, I have focused on clothing that dries fast. All clothing will be cold when wet, but some stays wet for much longer. That is why I gave up wool. It simply does not dry. I can get it wet on the first day of the trip, and it will still be wet on the third. I have moved largely to fleece as an alternative. It is just as “warm” when wet, but dries much, much faster. I have stopped using windproof fleece, which slows down the drying time.

In addition to the clothing of course, good moisture management techniques while in the wood are also important. If you are covered in snow, do not go near the fire because it will melt and make you wet. Good shell clothing is important because it will prevent the snow from making contact with your insulation. From my experience snow sticks very easily to wool and fleece. A waterproof jacket goes a long way even in dry snow. Similarly, I make sure to remove all wet and damp clothing before getting into a sleeping bag. The same thing that holds true to clothing insulation holds true for sleeping bag insulation.  

So that’s what I have to say about this based on what I have experienced. If something sounds too good to be true, it probably is. Use common sense, and ignore claims of magical performance.

The above techniques have worked well for me. Common sense has proven to work much better than magical fibers. When I am exerting myself and heating up, I don’t wear my rain gear so I don’t get my clothing wet with sweat. When it rains, I put on proper rain proof gear. My insulation is chosen so that it dries fast when it inevitably gets wet.

I am always happy to read boring studies, so if any of you guys are familiar with any interesting tests performed on different fabrics, please let me know.


  1. I've been following your blog for some time and while I find all your articles interesting and useful, these on the subject of materials should be widely distributed. I think you've done a good service that can save people a lot of money and potential misery. Seems every year the "outdoor" companies come out with a new miracle fabric gauranteed to keep you warm/cool/dry and possibly well fed all at the same time...even better than last years miracle fabric. I dont think they'll ever run out of customers who want to beat the common sense advice of wear what you can work in comfortably and carry rain gear. I spent quite a few years in the woods every week through my youth and beyond cutting wood, as that was my familys heating source. We always stripped down to just tshirts when the heavy work began, except on the most frigid days. At first I thought it odd that my dad brought clean rags and made us wipe the sweat off ourselves before we bundled up again, but after I didnt do it once or twice I understood. And those "silly" plastic ponchos sure seemed like a blessing after getting soaked once or twice on cold days. Anyways, thanks for all the great info and please keep it coming.

  2. Ummmmm...I've been hunting for 40 years, and wool is by far and away the best insulator dry or wet. Your hypothesis sets up wool as a straw man, easy to knock down. The question is more What would you rather have on when you get wet, wool or cotton or synthetic? Unlike cotton and synthetics, which wick away heat when wet, wool still acts as an insulator. When wet, it's imperfect, but when you're outside and wet, you're not searching for the perfect, but the sufficient. And wool gives enough heat to let a person light a fire, move to better ground, etc. My impression is that you're very inexperienced in outdoor living. I grew up with only wood heat, in rugged farm country, and I've seen wool pants frozen solid still insulating my legs to some degree. And that's all I needed. The Internet creates all kinds of armchair warriors, politicians, generals and experts. Don't be one of those guys. It's embarrassing.

  3. Ummmmmm...if you are telling me that your frozen solid wool pants were keeping you warm, I can only conclude that not only have you never been in the words, but also that you are either highly delusional or intoxicated at the moment.

    If you like wool, feel free to use it. However don't go around making unsupported allegations. The data is what it is. It's not my fault it does not fit your preconceived view of the world.

    If you have any contrary data to present, I would be happy to look at it. However, based on your assertion that you only wear wool, and that you allowed your pants to freeze, I can only conclude that you either live in a very warm climate or that you have very little experience in the woods.

    Like you said, there are many armchair woidsmen these days. I get the feeling, Mr Anonymous, that you are one of them. An easy way to tell is when you see a "woodsman" discussing straw-man arguments.

  4. What a silly young man you are. I used to wet wade in Big Fishing Creek in wool army pants, in October, because the wool was warm soaking wet. Data? I'm an avid lifelong outdoorsman, fishing and hunting from Alaska to Maine. Ask any guide whether wool is problematic. Yes, even frozen solid wool gives some thermal protection. As opposed to cotton or synthetics, which wick away body heat. If I revealed myself, you'd know I'm for real. But you are a young kid, a product of virtual worlds, digital data, make-believe. As you say, you're inexperienced in the outdoors. Why don't you take a pair of cotton BDU camo pants, a leading synthetic pant, say from Cabela's, and an old pair of woollies by LL Bean, Filson, Woolrich, etc, and go out to a local park, get them wet, and subject them to testing yourself. Wool is quiet, durable, rugged, and inflammable, unlike cotton and synthetics. It doesn't melt or catch fire when a campfire spark lands on it. I'm intrigued that your instinct is to call names and question someone who so obviously is experienced in the subject which you are discussing. Good luck with your career and life, young man. I'm willing to bet you have lots of conflicts with the people around you. And merry Christmas.

    1. You are indeed a funny man. You go around online anonymously insulting people and then "hide" your credentials when you are called out on it. If you in fact knew any guides yourself, you would know that they do not wear the clothing you are trying to push here.

      I convenient that you are "right" wihout having to present any data. If you bothered to actually look at my posts, you would see that I have been testing these materials for quite some time. Maybe you should try doing some tests yourself instead of spreading poor information. Half of the statements you make about the materials in question are clearly false. "Wicks heat away from the body..." Seriously? Perhaps you should look into how these fabrics actually work; or better yet, give them a try. It sounds to me like you have had very limited experience with modern clothing .

      You should broaden your horizons, look into advances in gear and technology, and spend some time with people who actually go out in cold climates. I assure you none of them climb Rainer, Denali, or even Washington in wool trousers and parka. Maybe you should ask them why.

      Going around online and anonymously posting absurd statements without any supporting information, and then referring to people as "young man" or "armchair woodsman" while at the same time hiding your "credentials" is very poor form.

      And just so anyone reading your statements doesn't accidentally follow your advise and get hurt, wearing a block of ice (whether formed around a piece of wool, fleece, or magical fabric woven by elves) will leave you just as cold and just as dead. The fact that you are asserting otherwise is disturbing, and shows a complete lack of understanding of textile properties, as well as being outdoors.

  5. Hahaha! It's painful to read this. I think a heated argument would keep me warm, pack a buddy next trip:-)