Head gasket designs and technology have changed over time with the advancement of materials and construction, and there are a few different types of head gaskets you will run in to if you need to replace this item. This does mean that when replacing an old gasket the new one may look very different to the one being replaced.
The older technology found on many of the older automobiles is usually a composite material made of graphite. This type of gasket has been known to have blowouts and has since been replaced with a newer more durable type known as MLS.
Multiple Layer Steel (MLS) is the head gasket type you will find on most of the automobiles today. The MLS will have two to five layers of steel and are coated with a substance similar to rubber. Beads around the combustion chambers and oil/coolant passages increase the sealing pressure of gasses and liquids, and elastomer coatings further increase the tightness of the seal.
Copper is another type of gasket you will find as well. We see this in high performance engines that are super-charged or turbo-charged as well high compression engines or ones that are using nitrous. There is a school of thought that copper is a good choice for its strength, conductivity and elasticity, and that is it a good heat conductor, making it very unlikely to experience a blow-out. When using a copper gasket a sealant must also be used. The main problem with copper gaskets is that they are the same thickness at all points and will not generally ‘mold’ to the variations between surfaces in the way a composite gasket will, making it less efficient at sealing by itself, meaning that some form of clamping is required. Therefore if the finish is not completely flat there is a good possibility of a head gasket failure.