Wool is a fiber made from the hair of sheep, goats, llamas or alpacas. While many find wool to be rather coarse, premium wool is very soft and comfortable against the skin. Extra-fine wool is super premium and is used in men's suiting of the highest quality knits. Wool has natural stretch and breathability. It moves when you do, keeps you warm when it's cold and cool when it's hot and adds natural comfort around the home. It's also fire resistant. Wool can be more comfortable unlined because it breathes and takes moisture away from the body. Synthetic lining material can't breathe the way natural wool does.
Fibers such as nylon or rayon are often blended with wool to add a novelty quality or decorative effect.