Incredibly dexterous while still providing the warmth you expect from mittens, the XG Mid Mittens boast an incredibly waterproof Hipora insert and low-loft Thinsulate insulation. Premium Anti-Pill Polyester Micro Fleece This ultra comfortable liner increases warmth and is designed to not pill with repeat use and wear. 100D 4-Way Spandex w/ PU Laminate 3M Thinsulate Insulation | 100g "Warmth without Bulk", this premium insulation keeps you warm by trapping and holding your body heat while keeping a low profile. Waterproof PU Hipora Insert Hipora is a 3 layer membrane that prevents water from coming in while letting moisture out. This premium fabric has a micro-porous structure with a polyurethane coating. The layers of material have tiny holes in it so water can't get in, but moisture will release out.