This is a topic that many people overlook. Having a good base layer is important for keeping you warm, dry and also healthy. One of the most complicated conditions to deal with in the field is a persistent skin infection which can arise from long underwear that are not easily cleaned or dried. Do not, under ANY CIRCUMSTANCES, wear cotton long underwear in a survival situation. The cotton will absorb moisture and sweat and quietly chafe your thighs, hips and any other points of contact into hamburger meat. There are different weights of synthetic base layers and I’ll let you decide how warm or cold you’re gonna be, but I’m gonna tell you the best place to start looking.
As I said, there are many weights to choose from, but when it comes to-quick drying, antimicrobial, easy cleaning, warmth to weight ratio and more- you can’t beat Capilene. Even the heavy stuff is still very dynamic and flexible. The lightest weight (silkweight) feels almost like you’re not wearing anything and even if soaked, can be dry in less than an hour if hung up. These fabrics provide chafing protection, insulation and moisture wicking all of which you won’t even know you needed until you don’t have them. One of the nice things about Capilene is that in comes in different weights, which can be worn in combination with each other. If you’re legs tend to be colder than your torso, you can wear a lighter top and a heavier bottom. Don’t feel locked in on any particular weight for your whole base layering system.
Take a look at your jackets and pants and see how much insulation they’ll provide for you and then consider which weight of base layer you’ll need in combination with your other pieces. Stay warm. Stay dry. Stay alive.