Polar Fleece:

A synthetic knit fabric with a pile on one or both sides typically made from either filament or spun polyester fibers. The fabric is knitted with tiny loops on one or both sides. The looped fabric then goes through a napping process, which cuts the loops into strands. The fabric is then sent through a combing process where the strands are groomed to stand upright.

Next, the fabric goes through a shearing process where the strands are cut uniformly to create the pile. The last treatment using heat to assure the fabric is anti-pilling. This is to protect the fabric from pilling - or allowing tiny balls of fabric to form on the surface. There are many grades of fleece available in the market. Fleece can vary in softness, thickness, density, weight, pile height, and look.