Fleece is one of the warmest, coziest fabrics around. Typically it’s made of polyester but can be comprised of any fabric. What gives fleece its...fleeciness...is that it’s soft with a deep pile—the raised surface, or nap, of textiles. Polar fleece, the most common kind found in cold-weather gear, has a soft nap and is super insulating. A sweatshirt or jacket made of the stuff will be your go-to garment when things are chilly.