Polartec Classic 300 is the heaviest Polartec fleece fabric, designed to provide a warm thermal layer for very cold conditions. It's made from 100% polyester, meaning that it's durable and machine washable. The fabric is breathable and can also have a water-resistant layer applied to it.
Heavy weight fleeces are best used in cold conditions as a top layer or under a waterproof top layer. They're there to keep you warm, while the breathability of the fabric will also help keep you dry.
The 100% polyester surface is pebbled, creating air pockets that trap warm air in order to retain your body heat. This provides outstanding warmth without needing too much fabric, reducing the weight of a garment. The fabric also offers excellent breathability, dries quickly and is fully machine washable.
Polartec Classic 300 on Polartec.com