WATERPROOF - BREATHABLE - WINDPROOF ISOWIND material with microfleece lining. ISOWIND is an elastic, polyurethane membrane which is fused onto microfleece. This membranous material provides optimal thermal regulation and prevents cold hands. The ISOWIND membrane is absolutely waterproof, windproof, and yet extremely permeable. Because it is a membrane and not a fabric coating, the ISOWIND material will not lose its waterproof property.