It’s Cold. Thoughts About Thermal Underwear.

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Wintertime is bringing many questions from readers about underclothing that’ll keep you warm.

In a post last week, I professed my love for the Uniqlo line of undershirts (including the toasty Heattech line), but since I’ve been exchanging emails with readers about the topic, I thought I’d consolidate the information here.

Here are some of the questions:

1) Thanks for the website, always great. I am an avid wearer of undershirts, mostly for their ability to add life to a dress shirt and give a bit of comfort.

Soon I will be moving to the frigid northeast (I’m from Florida and cold natured) for a job and was wondering if there are any undershirts that particularly excel at layering.

My limited experience with under layers is that they bunch up, can be heavy, and are a whole different beast than regular undershirts. As often is the case, the internet provides more confusion than answers, any thoughts are appreciated.

2) Have you tried Rocky’s Thermal Underwear sold at Walmart?  I was wondering what you think of it.  

I need some thermal underwear to work in the dead of winter for places like North and South Dakota and Minnesota.  Usually it goes down to -40 degrees easily.

3) Does anybody make a white, long sleeve, v-neck merino wool undershirt? I’m looking for something to wear under nice button-downs when it’s freezing cold outside.

I prefer wool to synthetic materials as it feels better and my skin doesn’t usually agree with synthetics.

4) So, it’s getting cold outside. I am currently searching for long sleeve heather grey v-neck thermal underwear.

Any suggestions? Also, what are your thoughts on how thermal underwear affects the lay and fit of the shirts over top of them?

Whew! That’s a lot of questions.

Before we get to the recommendations, I thought it would be fun and educational to share some very interesting information about thermal comfort.

One of the readers above shared an incredibly informational article from Low-tech Magazine written earlier this year that discusses the topic of insulating the body.

I thought it was fitting since thermal underwear is designed to help keep us warm, so let’s learn a little about the topic before we dig into thermal underwear options.

Looking for a PhD in thermal comfort?

You’ll get it if you read the whole Body Insulation Thermal Underwear article, but I plucked some excerpts from it that I thought were most relevant to the topic at-hand.

A person wearing briefs (0.05 clo), light socks (0.05 clo), a t-shirt (0.10 clo), a heavy shirt with long sleeves (0.25 clo), a sweater (0.30 clo) and long pants (0.30 clo) is protected by a total thermal insulation of 1 clo, meaning that this person will remain comfortable hanging out in front of the television at a temperature of 21° Celcius (70°F).


The US Army found in the 1960s that a maximum of 4 to 5 clo-units could be worn for a man to remain mobile and dexterous enough for military tasks.

Additional clothing weight thus limits our freedom of movement, and even couch potatoes have to get up from time to time.


One layer of thermal long underwear allows you to turn down the thermostat with at least 4° C, saving up to 40% on space heating energy.


And, last but not least, it can be worn in layers, further improving upon the insulation value: more air is trapped using several thin layers than by a single, bulkier layer.

According to the US Air Force Survival Book, one layer of long underwear (long pants + long-sleeved t-shirt) equals a clo-value of 0.6, while two layers of long underwear add a clo-value of 1.5. In other words, the clo-value more than doubles by using only two layers.


Another indication for the additional energy savings potential of high-tech long underwear are the clo-values of different materials.

According to the “Handbook of technical textiles”, the warmth/weight ratios of pile fabrics like polyester and acrylic are 2.5 to 8 times higher than those of woven and knitted fabrics like wool or cotton (materials used for traditional long underwear).

Quilt battings like Thinsulate offer warmth/weight ratios that are 13 to 17 times those of cotton and wool.


Cotton might have a relatively low insulation value, but a full layer of cotton long underwear will still add at least 0.4 clo to your thermal comfort – enough to lower the indoor temperature by 2.5° C and save more than 20 percent on heating bills.

Using wool can more than double this potential to about 1 clo for a full layer of long underwear (allowing for an indoor temperature reduction of more than 6° C).


Wool made a comeback as a material used for hiking and mountaineering clothes in the mid-1990s, at which point Icebreaker was the first manufacturer to position itself in the market with woollen thermic underwear.

The company uses wool from the merino sheep in New Zealand, which produce some of the finest and softest wools available.

Patagonia also offers a series of merino wool underwear, and several European manufacturers (Mammut, Woolpower and Helly Hansen) mix merino wool with synthetic materials.

This leads to more durable clothing – wool wears out much faster then synthetic materials.

An important advantage of wool over synthetic (and over other natural) materials is that it maintains a good smell for a very long time.


The thermal properties of clothing drastically degrade when they become wet, either by sweating or by external moisture.

This can be very dangerous if you are physically active in a cold outdoor climate because during a resting period your body can quickly lose heat, possibly leading to hypothermia and death.


It is telling that one defence mechanism of the body against cold is to increase its heat production.

This happens first by muscle tensing and ultimately by shivering, which can increase body heat production by up to five times

Ok, now that we’ve got more information about how to maintain your body temperature, let’s dig into some of the questions and product recommendations that were made.

In reviewing all four email exchanges, plus thermal underwear recommendations from Ask Andy About Clothes Forum Members, I was able to compile the following list of thermal underwear recommendations:

  1. Icebreaker
  2. Carol Davis Sportswear (was at (Recommended by Antonio Centeno. Made in USA.)
  3. Patagonia capilene baselayers
  4. Wickers
  5. Mammut
  6. Woolpower
  7. Helly Hansen
  8. Brynje underwear
  9. Uniqlo Heattech
  10. REI / Sierra Trading post: Polypropylene and Wool product options
  11. Cabelas – several temperature/activity levels of reputable long underwear
  12. Chock
  13. Duofold Union Suits over Silk Base Layer
  14. J.E. Morgan
  15. Thermasilk
  16. Healthrite (from
  17. Under Armor’s Thermal Underwear / Cold Gear
  18. Polypropylene and Rochelle or waffle knit thermal underwear
  19. Army/Navy store

Here are two excerpts from Ask Andy Forum members that I thought were very helpful as well:

Only major rule you need to know is do not under any circumstances wear cotton as your base layer (you will sweat and then freeze).

Your bottom layer needs to be something moisture wicking.

At -40 I was wearing Under Armor thermal for a long sleeved shirt, then a nike dri fit t-shirt, then a cotton t-shirt, then a hoodie, then a cabelas parka and finally a Marmot lightweight rain shell.

For pants it was the Under Armor long underwear then jeans, then soft cargo pants, and then down snowpants.

That combination was easily much warmer than a $1,000 military parka and has the added benefit of each individual piece being able to be used throughout the year for various purposes.

They [cotton fibers] lose their puffiness and sort of collapse, making them denser. Cotton fabric thus becomes hard and no longer retains body heat.

I have very sweaty feet; they are just as damp regardless of the material my socks are made of. But on my feet even the softest cotton socks become abrasive (blisters!) and do nothing to keeps feet warm.

If I wear synthetics or wool, my feet are damp, but the socks stay soft, and my feet stay warm.

In addition to recommending Icebreaker, Uniqlo and Wickers, I provided the additional thoughts to the reader who asked question (4) above:

I haven’t tried products from wickers or icebreakers yet, but I have tried the super thin (and warm) heather grey long sleeve v-neck heattech undershirts from uniqlo and they are pretty fantastic.

they are made with acrylic, a synthetic wool substitute, and the blend uniqlo uses feels really nice on the skin. it goes without saying (but I’m saying it anyway) that they keep you nice and warm.

to your second question, if you wear a thinner product like uniqlo, you wont affect the lay or fit of your outer shirts.

personally speaking, I think wearing traditional “thermals” (the waffle knit ones) really is only needed in more severe cold weather in outdoor applications.

I’m not sure where you live, so waffle-knit thermals may actually needed, but I’d try one of the above products first. 

Men’s Thermal Underwear Video

And finally, my good friend Antonio Centeno from Real Men Real Style did a great write-up and video on Men’s Thermal Underwear.

Here’s his video recapping his recommendations:

7 thoughts on “It’s Cold. Thoughts About Thermal Underwear.”

  1. Hi tug,

    I’ll start by saying, I’ve searched the internet A LOT to find the best clothes for my situation, but there never seems to be a clear answer.

    My job requires me to sit through about 10 hours or longer in temperatures roughly below 30 down to -10, and doing almost no physical activity at all.

    I just want to know what the best clothes are for extreme cold and no physical activity.

    Please help. I’m very cold.

    • heya matthew,

      if you need some help staying warm, i’d say check out the heattech under-gear from uniqlo. it’s as warm as wool, but smoother and softer on the skin.

      outside of heattech (or wool), i’d say look at for some other items designed to help you stay warm.

      #1 rule of thumb for staying warm, is to layer clothes. more thin layers is better than fewer thick layers.

      plus, you’ll likely be more comfortable.

      heattech and/or — check’em out and let me know if you find something you love!

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  4. When I was 15, my parents sent me to a kind of reform school in the woods. Think Outward Bound meets One Flew Over the Cuckoo’s Nest. We lived outside in cabins with walls made of thin plastic sheeting. In the winter I wore basic cotton thermals from Sears as a base layer. I sweated when working in them–cutting wood, paddling canoes–, and certainly didn’t freeze afterward.

    Today my base layers tend to be wool or synthetic blends I buy from Patagonia. Much better than Sears cotton thermals. But if all you can afford now is cotton, I can attest that they do help keep you warm and won’t freeze if you sweat in them.

    • hey brent! thanks for sharing that info.

      i too wore basic cotton thermals during the winters when growing up. at the time i lived on the northern side of the east coast and winters got kinda cold – plus we went snowmobiling a lot too. I recall sweating some, but never freezing afterwards either.

      i think that is what would likely happen in more extreme cases, and not during general everyday wear. i totally agree with you – for those on a budget, there is definitely no need to go out and by more expensive wool or synthetic thermal base layers.

      after all, we are in a recession and there are lots of folks without work. thanks again for sharing!


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