I know basically nothing about fabric blends other than if it says “dry clean only,” it doesn’t get bought by me. :-) So... if I buy my husband long underwear that is 100% cotton, how warm will that keep him compared to the long underwear he already has that is 80% cotton and 20% polyester?

I used Long Johns a lot early in my career and found that I could not tell the difference between 100% and the blend of 80-20%. Everyone has their own preference on what works for them. Some even prefer wool. Itchy on me. I would scratch like a dog in a flea circus.

What I can tell you is the as you get warmer with the cotton Johns and start to sweat a little, the cotton will wick the moisture away and you won’t get a cold clammy feeling and you can sweat even when it’s cold. 80% should be OK but I would not go lower. Polyester will not wick moisture.

Next, remember cotton can shrink a lot when washed. You don’t want them getting tight on you. I would buy them 1 size larger and that seemed to work for me. I don’t know how to stop that but I someone else can help there.

Any insulation works by trapping closed air cells. This stops the heat from being pulled away from the body. Both cotton and poly will do that but poly does not wick moisture well.

And lastly, remember it can depend on the manufacturer. The waffled style seemed to be the best for me.

Thanks, WoW! He has an 80-20 blend now. I just wanted to make sure the 100% cotton will keep him as warm as the ones he has now. It looks like they might even be better? That would be great. Now if I could just get him to start wearing his scarf...

Cotton is not as warm as some other things. I am a camper, so I need to know these things. I have cold feet, so the trick is to have a layer of something that will trap the heat but wick away moisture. I have polypropolene socks as an inside layer and wool on the outside. Even when wet, this type of layering should keep you warm.

We always bring a change of socks and underwear to change into, before bed and for the next day. Even if you don't notice, cotton absorbs the moisture and dries slowly, so it doesn't do much good if you sweat a lot, and will make you cold once you wind down your activities.

I've heard silk is good, but it is expensive, and requires careful washing.

You know boys will be boys.

Hemen don't button up coats, ware hats, or ware scarfs and Lord, don't let anyone know they are wareing Long Js.

Wimps.

Poly was added to give them durability.

Cotton is not good for long underwear. Polypropelene and other blended synthetics work so so much better.

None of the long underwear I have requires careful washing - just no drying.

Silk isn't better - it just feels nicer on the skin. Silk long underwear can be washed - it seems wrong but it works fine and it can even be thrown in the dryer. I use it when skiing most of the time because when doing active sports it seems much more comfortable but there is no doubt in my mind that polypropelene and fleece are the best for keeping warm. Fleece is also a polyfiber and dries super fast and holds in heat. I sometimes run outside in weather under 20 degrees and it works. Cotton gets wet and stays wet and then you're colder and colder as the day goes on.

Polypro wicks moisture and seems thicker and warmer. I love it.