3M Thinsulate - 3M Thinsulate is warm, lightweight, powerful, and thin. The extremely fine microfibers in Thinsulate help to trap air and block body radiant heat loss, making for an incredibly efficient insulation while still allowing internal moisture to escape. A high warmth-to thickness ratio also enables reduced bulk and advanced freedom of movement. In other words, Thinsulate material traps more air in less space, giving your foot more room to breathe.