Thermal clothing is made from two-ply material, typically with layers of cotton, wool or synthetic fabrics such as polyester. The base layer’s purpose is to draw moisture away from the skin in a process called capillary action or wicking.

This is where the forces of adhesion, which cause water molecules to stick to other surfaces, are greater than the forces of cohesion, causing water molecules
to stick together.

This means that sweat is drawn into the narrow spaces between the clothing’s fabric fibers, just like a paper towel absorbs water or a candlewick absorbs fuel. The moisture is then drawn to the outer layers of the fabric, where it can evaporate much faster and won’t leave you feeling wet and cold.

The outer layers also provide insulation, trapping heat so that you stay warm in cold temperatures

Adding a thermal underlayer will keep you warm and dry on cold winter jogs