Spiral Wound Gasket comprise a mix of metallic and filler material. Generally, the gasket has a metal (normal carbon rich or stainless steel) wound outwards in a spiral (other shapes are possible) with the filler material (generally a flexible graphite) wound in the same manner but starting from the opposing side. This results in alternating layers of filter and metal.
The filler material in these gaskets acts as sealing element, with the metal providing support.