Willseal® 600 is a pre-compressed, self-expanding foam joint seal, engineered to perform as a highly flexible, weather-tight, primary seal in vertical exterior applications. The high-density polyurethane foam is impregnated with a modified flame retardant, hydrophobic, UV stable acrylic resin and treated with a pressure-sensitive adhesive on one side for ease of installation. Willseal 600 self-expands to fill the joint creating an elastic, vapor-permeable, weathertight seal.