PTFE filled with other materials such as graphite, bronze, glass and carbon. Each have their own advantages: "Graphite filled PTFE" Exceptional chemical resistance and is compatible with most hydraulic fluids. Outstanding performance when used for hydraulic/pneumatic compression type rod and piston seals, bearing bands and rotary applications. Low coefficient of friction compared to other filled PTFE materials. Higher flexural modulus and surface hardness than unmodified PTFE. "Bronze filled PTFE" This filler has better wear, creep resistance, and higher thermal conductivity than glass fiber with PTFE. The compound is easily machined, but has poor chemical resistance in the presence of acids and alkali. Useful in applications which undergo high mechanical loads or high-speed rubbing contacts where the bronze filler supplies the strength and conductivity to carry away excess, unwanted heat. "Carbon filled PTFE" Different filler percentages will change the properties. The two basic materials used in these compounds, by themselves, are very questionable. PTFE has good frictional properties including low wear rates and good elasticity. The carbon filler is brittle and has low wear properties. Both fail at high loads and increased velocities. When both elements are formulated and properly blended together, they become an extremely good material for use as seals and rings in the reciprocating compressor industry. The properties increase several hundred times. Wear resistance is changed dramatically compared to virgin PTFE. The type and percentage of carbon is critical to material performance. For optimum wear properties, the filler percentage is also important. Lower percentages are easier to machine but do not perform as well in service. "Glass filled PTFE" Glass fibers have the least effect on chemical and electrical properties and add greatly to the mechanical properties of unfilled PTFE. Addition of glass improves compressive properties by as much as 40% and improves wear resistance greatly. These compounds resist acids and oxidation but can be attacked by alkali. It is heat resistant and have better mechanical properties than standard PTFE.