Fleece is a synthetic fabric made out of 100% polyester. It can be combined with rayon or spandex, or with natural fibers (cotton or wool). It is highly insulating (4 times the insulation of cotton). It is lightweight, soft to the touch, dries quickly, and continues to insulate well even when wet, making it perfect for cold weather activity. It is incredibly durable and long lasting, does not absorb water or odeurs, do not break down in appearance, and it is hypoallergenic.