Great for sealing the underside of centerboard trunks, transom flaps or rudder fairings on larger boats. Mylar (with Dacron on one side for glue/epoxy to bond to). 2-inch size (SS50) is commonly used for centerboard gaskets (two separate strips overlapping). 3-inch size (SS75) is commonly used for centerboard gaskets (on strip slit down the middle or two separate strips overlapping). 6-inch size (SS150) is commonly used for very large centerboards, rudder fairings or transom flaps.