If you're going on an adventure at a high altitude or on an excursion in cold weather thermals could be the ideal option to keep warm and cozy during cold conditions in the mountains. However, experienced trekkers as well as outdoor experts recommend against wearing thermals while trekking even though they're ideal as a base layer, they can cause harm if worn on hikes. Thermals are an essential part of high-altitude trekking clothing however, many trekkers believe they should not wear thermals during the trek, despite being intended for post-trek clothes. There are a variety of reasons for this, but to better understand them, it is essential to know how they function they function as a base layer in cold weather conditions, and directly touch skin to conserve body heat and stop loss of heat; polyester is often blended with other fabrics like Lycra or wool for additional comfort and flexibility. Ultimately, thermals fall into two categories referred to as Dynamic and static layers that are what our Trek Guide, Nitin Rana describes as Static and Dynamic thermal layers, respectively.
Thermal Trap Body Heat
The purpose of thermal clothing is to trap body heat which is beneficial when you aren't moving a lot, for instance when you sleep in tents. However, during activities like trekking, your body produces sweat and heat that the thermals can't capture quickly, resulting in excessive sweat accumulation within them, leaving you feeling uncomfortable and sticky after a while.
Wet Thermal Creates Risk.
Thermals that are saturated with moisture as a result of sweat or sudden precipitation could take a long duration to dry out, particularly in mountain areas with low temperatures and humid air. Closely rubbing against your skin the wet thermals can rapidly drain your body's heat, while increasing the risk of hypothermia during periods of apathy or when the night approaches, temperatures drop dramatically.
Ventilation Problem
The slender design of thermals and use of materials specifically designed to trap heat can limit airflow considerably, which can be beneficial when you are not physically active. However when you're performing physical activities it can result in your body's temperature to rapidly increase, leading to sensations of heat stress, discomfort or even dehydration.
