Thermals are an essential warm layer on any high-altitude trek.
But what many trekkers don’t know is that you should not wear your thermals while trekking, no matter how cold the weather is. Thermals are meant to be worn only after your trek.
There are many reasons behind this.
To give you an idea, let’s talk about how thermals work.
How thermals keep you warm
Thermals are used while layering in cold weather. They are the layer closest to your skin.
They act as an insulator between your body and the surrounding cold air. They trap body heat and prevent heat loss.
They are generally made with polyester. It can also be blended with other fabrics like lycra or wool to give extra comfort and flexibility.
The types of thermals
There are two kinds of thermals. Our Trek Leader Tanmay Bain, categorizes them into Dynamic and Static.
Dynamic thermals are designed to be breathable and allow comfort to your body. These thermals can be worn during the trek. They are stretchable and made of synthetic material. Dynamic thermals are thin but they do a great job in keeping you warm. The best part is they absorb sweat and dry quickly.
Static thermals are the thicker ones, and are mostly made of wool. If you wear these while trekking, they will make you uncomfortable.
Let me elaborate.
Why you should not use thermals while trekking
The principle to follow while layering for a trek is that the first layer in contact with your body should not retain sweat/moisture, and should allow for free movement.
Here’s why thermals are a bad choice for this.
1. Thermals don't dry quickly
Trekking is a strenuous activity. So inevitably, you start sweating. Even if you are trekking in cold weather at an altitude of 12,000 ft to 13,000 ft.
The sweat will make your thermals wet. As static thermals are made of merino wool, cotton, and a mix of synthetic and polyester, they don’t dry quickly.
So if you use your thermals during the day while trekking it will not dry by night when you will need it the most. Wearing wet thermals will only make you feel colder.
2. They make you sweat more
Wearing thermals while trekking will make you sweat more than normal. This causes dehydration which is fatal at high altitudes, where AMS is a looming threat.
3. Sweaty thermals can cause skin rash
If you sweat into your thermals while trekking, and wear that over a long time, they can make your skin irritated and prone to rashes.
4.They restrict ease of movement
As thermals work as insulators, they are designed to wrap around your body tightly to trap heat. This can restrict your body from moving freely, which is uncomfortable while trekking.
Instead of thermals, you can wear a full sleeve t-shirt in summer treks. In winters, you can have a t-shirt along with a fleece or down jacket.
If you are someone who is not resistant to cold, you can go for dynamic thermal. These allow free and comfortable movement of your body and are quick-dry.
So when should you use thermals
Thermals are meant for use at night when the temperature dips in the mountains. If the day temperature records 10 to 15 degrees Celsius, it is likely to go down to negative at nights. This is when you will need the most warmth.
On a normal clear day, you can take out your thermals when the sun goes down at the campsite. The idea is to wear it while your body is still warm.
Thermals work as a heat retainer by blocking the cold from getting inside. It will keep you warm till you get inside the tent and then to your sleeping bag.
If you are investing in a dynamic thermal, it can be worn at any time of the day.
When you are using thermals in the evenings and at night, you can tuck it inside the gloves you are wearing to block any cold air from getting inside. You can do the same with your socks, tucking your thermals into them. This will keep you warmer.
Where to buy thermals
Dynamic Thermals are a must if you are regular trekker at high altitudes. Though the price is higher, they are worth investing in.
There are many brands that make dynamic thermals such as Columbia, Nike, and Northface. The multipurpose Columbia dynamic thermal costs approximately Rs 3,999.
At Decathlon, these dynamic thermals start at Rs 1,799. They have static thermals as well. The price here is lower than in most stores.
Static thermals can also be bought from any local shops. If you’re not a regular trekker, these will do. They start at approximately Rs 400.
So there you go. I hope I have answered your question on whether to wear thermals while trekking. Remember these tips when you go on your next trek!
You can also read this article to know how to layer for a Himalayan trek.
If you’ve got any more tips or suggestions about thermals, drop in your comments below.