[aussiblue]

and at http://www.babcox.com/editorial/cm/cm100178.htm

The ultimate head gasket design today is multi-layer steel (MLS), which is used on Ford 4.6L V8s, other Ford engines, as well as Chrysler, Honda, Mazda and others makes. This design typically has three to seven layers of steel. The outer layers are usually stainless spring steel, embossed and coated with a thin layer of nitrile rubber or Viton to provide extra cold sealing. The inner layers provide added support and thickness.

MLS gaskets are extremely durable compared to other types of head gaskets because of their all-steel construction. They won't burn through, and they won't relax and take a compression set that can lead to leaks and sealing problems. MLS gaskets also reduce blowby and improve compression by reducing bore distortion in the cylinders (less load is needed to seal this type of gasket.) But MLS gaskets require a special type of head bolt that stretches when it is tightened ("torque-to-yield" or TTY head bolts, which should not be reused). They also require extremely smooth surface finishes on both the cylinder head and engine block to seal properly.

Aftermarket MLS gaskets have also been introduced as replacements for some problem engine applications that need a more durable head gasket. These include the Toyota 5VZFE 3.4L V6 truck engine and the 2.0L Dodge Neon. On both applications, the MLS replacement gasket works better than the OEM gasket - and requires no special surface finish because an extra thick coating provides the proper cold seal.