Extreme weather conditions require extreme clothing, and nothing beats top quality thermal underwear when it comes to keeping warm. Modern thermal underwear can be composed of multiple thin layers of fabric to trap more body heat and still allow the skin to breathe. Polyester, Wool, and silk are all commonly available materials, but what is the best thermal underwear for extreme cold outdoor conditions? Here we have a head-to-head comparison of the three main fabric types.
Polyester is a man made fiber that is fairly inexpensive, and is becoming more and more commonly used in thermals. It does a pretty good job of imitating natural fibers like wool, but unfortunately it has a habit of trapping odors. The combination of ammonia and bacteria that live on your skin quickly results in smelly clothes. Poly-cotton and polyester-wool blends can be a reasonable compromise, being comfortable and fairly breathable. However, when the polyester ratio in thermals goes above 20 or 30% you will find it has a distinct plastic quality. My verdict: Good for a budget solution, and great for short term sports or running underwear for women or for guys, but not for the serious outdoor enthusiast. Although synthetic fibers are constantly advancing, these are not the best thermal underwear for extreme cold situations. Still, this might change in the next few years. We’ll see.
Silk is not usually associated with hard wearing underwear, but silk long johns for men and women are not a bad choice. Silk breathes well, and has a delightfully smooth and cool feeling when worn under heavier outer clothes. In a single layer silk is not terribly effective as insulating underwear, but thanks to its very fine fibers and resulting light fabric it can easily be fashioned into 2 or 3 layer composites. Quite often silk is combined with wool or a cotton layer to increase its weight and thermal properties. Although expensive, silk composite is often regarded as the best thermal underwear for extreme cold where you can stay fairly dry.
Fine wool, most often from Merino sheep farmed in Australia and New Zealand, is probably the ultimate material for thermal underwear. In my opinion pure wool is simply the best thermal underwear for extreme cold hands down. Superfine wool is very smooth and light weight (nothing at all like a scratchy woolen jumper!) and keeps you amazingly warm. For people like me who are into outdoor sports it is ideal because you don’t ever get soaked in sweat, and if you do get wet through you still don’t freeze. Wool doesn’t hold water like a sponge like cotton does, so you still end up with air pockets trapped in the fabric even when it is wet – the result is that it still insulates you. If you are into skiing, hiking, or any other adventure sport then woolens are the best thermal underwear for extreme cold no matter where you are. The only downside to pure wool thermals is that they cost a lot more than polyester or cotton, but once you have worn them you will appreciate it as money well spent. Be wary of really cheap wool-polyester blends that advertise “contains pure wool” or “real wool” and similar – have a look just how much wool they actually contain, since quite often the fine print reveals that they might only have 10% wool with the balance being a cheap and nasty polypropylene filler. A small percentage of synthetic fiber can make woolens more elastic, but above that 20-30% threshold you lose effectiveness.
Remember that you generally get what you pay for, and super cheap outdoor clothes are rarely worth it. Online store like Amazon are a great place to shop for the best long underwear for cold weather and other great camping gear, so keep an eye on the “featured products” list down below to snap up the bargains that come up from time to time.