Thermal Underwear & Layering for Trekking

Thermal underwear can be your best friend on a trek! It's very lightweight and provide a lot of extra warmth anythime you need it. There's a few options, basically between the thin Polartec-stuff and the thicker wool/fleece stuff. Have a look here:

A set of polypropylene or Polartec underpants + undershirt can come in handy under pretty much any conditions. During daytime trekking when "real thermals" are too hot, or during cold nighttime. Good trekking underwear is important because it is the fabric closest to your skin. For trekking in the (extended) cold season in the Himalayas, October to March, a set of thermal underwear beneath your trekking trousers and trekking jacket is highly recommended to counter the cold, high-altitude conditions.

And if you are going high-altitude above 4000 meters / 13,500 ft or so - and plan to be there for a few days or more - you'll need thermal underwear all year round in the Himalayas.

By all means, DO NOT go trekking in a cotton t-shirt. I know local people in Nepal and India swear by them and street vendors are pushing you hard to buy them, but on the trekking trail you will sweat and cotton quickly becomes wet - and stays that way. It sticks to your body and besides being uncomfortable and more heavy, you increase the risk of catching a cold. Be nice to your body and get proper underwear.

Polypropylene (left) or Polartec (right). Both materials are very thin, but still providing good extra warmth for your body, while allowing it to breathe.

and matching undershirts

Polypropylene (left) vs. Polartec (right)

Thermal layering trousers/pants (tights)

And for dedicated trekking in the cold season, November to February, you need thermal layering beneath your normal trekking clothes. Even during daytime trekking, it gets cold above the 3000 meters / 10,000 ft marker.

To keep it simple, let's look at wool vs. fleece thermals. We all know that wool feels warm and stays insulating when wet. And that it can be itchy. It absorbs water so wool will become more heavy when you are sweating. Synthetic fibers, basically being plastic fibers, don't absorb water, and so stays more lightweight when wet. But for thin tights, it's not much weight we are talking about in the first place. So wool is totally acceptable. But it's itchy!? Not necessarily. There's a certain wool called Merino which is much finer, and too small to irritate your skin. Merino wool from the Icebreaker company is really state of the art and loved by many trekkers. Just ask around.

Wool (left) or fleece (right)? The choice is yours!

And yes, I actually used the word "love" about a sheep hair products! All hail to the sheep! Once you have your proper trekking underwear, also check out my trekking trousers / pants recommendations here.