Aclima HotWool 230g and 400g garments are made of terry knitted fabric. For people who work extensively outdoors, this is a definite favorite. The terry fabric is a wool blend where wool makes up the largest component, and it is mixed with other fibers to make the garment thicker and more durable than pure wool. The fabric offers fantastic insulation, owing to the loops on the inner side of the fabric, which holds a great amount of air. This type of underwear is used by the military because it is durable, itch-free, and gives excellent insulation.