Carbon foils are stocked in five basic forms: Pyrolitic graphite - a strongly anisotropic, high density, high purity material manufactured by Chemical Vapour Deposition (CVD). It is non porous and self lubricating, lightweight and shows excellent thermal shock resistance. It can be easily machined with normal metalworking tools. Flexible graphite - an exfoliated material which is mechanically bonded to form thin, flexible sheet. It is commonly used as a gasket material for corrosive or high temperature service (up to 600C in air, 2500C in an inert atmosphere). Rigid graphite sheet - a rigid form of graphite. The exceptional corrosion resistance and high temperature properties of graphite make this material suitable for applications as diverse as heat exchanger blocks for chemical process plant and arc furnace electrodes used in steel manufacture. Highly Oriented Pyrolytic Graphite (HOPG) - a highly oriented form of high purity pyrolytic graphite which diffracts x-rays and neutrons with greater efficiency than any other material. Vitreous or Glassy Carbon - is available under a separate heading. This material has high flexural strength with zero open porosity and, hence, a low permeability to gases. Glassy carbon has excellent resistance to a wide range of aggressive chemical enviroments and can, therefore, be used as an alternative material to precious metals for laboratory equipment and, for example, for electrodes in polarography.