Ultra-Seal is Mr. Gasket premium valve cover gasket material. It's manufactured from a high density cork and rubber blend with a black latex coat applied to the outside to help seal minor flange irregularites and eliminate oil leakage. It creates a positive seal by controlled swelling of the gasket material when exposed to hot oil. For original equipment replacement, high performance street, drag race and oval track use. Sold as a pair, these gaskets are .187 inch thick.