This depends on the environment of the application. The spiral wound gasket is semi-metallic, comprising of a spirally wound v shaped stainless steel strip and a non-metallic filler material, such as graphite or PTFE. Also on the gasket, is a solid outer ring used for centering and controlling compression. This minimizes the risk of material creep through over-tightening. For the toughest conditions, spiral wound gaskets are available with an additional inner ring. This protects the windings (particularly the filler), from contamination, or attack by the product travelling past the pipeline joint.
There are many different brands on the market such as Klinger and Flexitallic, all of which have their own strengths and advantages. As the spiral wound gasket is made using combination of materials, you need to consider operating temperature, pressure, chemical compatibility and long-term cost-effectiveness of more robust products over cheaper but less reliable alternatives.
Kemtron stocks a wide range of gasket brands for all your requirements. If you are looking to reduce emissions you should consider the Fishbone gasket, which has the lowest leak rate amongst metallic gaskets in the market today.