Butyl rubber surrounds are superior to foam in two important ways. First, the butyl rubber resists moisture and will not dry rot, providing years of service. Second, the rubber surround, due to its superior damping characteristics will greatly reduce cone break up and ensure low distortion. These woofers are ideal for replacing and upgrading old, worn out drivers. They all feature a polypropylene cone, vented pole piece, foam gasket, soft poly dust cap, and stamped steel frame.