Fel-Pro PermaTorque SBF Head Gaskets

"Stopper'' layer provides superior primary combustion seal

So, why use a Fel-Pro multi-layer steel (MLS) head gasket? Because more power per cylinder, higher operating temperatures, and thinner head and block castings demand a new kind of gasket. MLS gaskets are stronger, more forgiving, and capable of sealing despite extreme horizontal and vertical motion between the head and block. Such motion results from thinner, lighter aluminum head castings that are more susceptible to thermal expansion; modern computer controls that allow OEMs to dramatically increase engine efficiency/output; reduced clamping forces that prevent local stress points and cylinder bore distortion.

MLS technology was developed to overcome sealing challenges. The number of layers in an MLS gasket ranges from two to five, depending on the engine's sealing characteristics. Generally, the more layers, the more motion the gasket endures. There are multiple solid layers of heat-treated stainless steel separated by a very thin rubber coating, and the layers are either active (absorbing motion between the head and block) or shim layers (giving the gasket its correct compressed thickness).