Comprised of multiple embossed layers of stainless steel with the outer layers utilizing a Viton rubber coating. Compressed thickness is 0.040". W9 Heads. Cometic MLS (Multi-Layer Steel) Head Gaskets provide maximum sealing performance for todays high output engines and require no sealants. MLS gaskets are ideal for both aluminum heads to aluminum blocks and aluminum heads to cast iron blocks. They can withstand the shearing force created by the two materials. MLS gaskets have increased strength because they are comprised of multiple layers of stainless steel; which also creates the ability to rebound and resist corrosion. The outer layers are embossed and coated on both sides with Viton (a flour elastomer rubber based material that is heat resistant to 250 C/ 482 F). Viton is designed to meet the demands of a variety of harsh sealing environments, load conditions, and surface finishes. The center or shim layer is uncoated stainless steel, which can be varied to accommodate multiple thickness requirements.