HydroBlock is a waterproof and breathable coating that is exclusive to the Obermeyer brand. Featured on much of their outerwear, from toddlers to adults, this polyurethane coating is designed to keep you warm, dry and comfortable. The microporous nature of this coating allows any garment it is applied on to keep a great level of breathability. This is especially important when skiing or engaging in other active winter sports, as sweat can drastically lower your core temperature if it is not allowed to evaporate.