Brush Seals are made from polyproylene filaments packed densley together to prevent airborne particulates from passing. Brush is wrappped around metal and kept in place by a crimped peice of metal called a spline. The filaments will not hold water or freeze. Brush Seals prevent air and dirt contamination and have sound dampening properties. Ideal use for overhead garage doors, entry / exit doors, dock levelers, docks, etc.