The warmest arm warmers on the market! Made of Polartec®Powerstretch. This material is very breathable and offers warmth without much weight. It is wind and abrasion-resistant, and is machine washable without pilling. Your arms take a big part of the wind and cold on morning winter rides. Combine these with our new Windvest and you will conserve a lot of energy trying to stay warm! What makes our fleece lighter but warmer than others? Pretty simple really, we got our idea from the birds. Their feather down keeps them warm. Down feathers are hollow so not only are they light, but they trap warm air. We use this same principal in our fleece. The fibers we use in our fleece are hollow so you stay warmer than other fleece! Sizing Chart