The stretch fit and fleece lining make the Castelli Pioggia 4 a warm, comfortable bootie in dry conditions, and it's made for maximum protection in wet conditions as well. The Pioggia shoe cover is completely waterproof, with sealed seams, a waterproof zipper, and a silicone-sealed top edge to keep water from entering. The PU-coated fabric is also backed with fleece to make this bootie warm in the coldest conditions, while the high stretch gives it a close, comfortable, and aero fit.