Virgin PTFE is reinforced with 25% glass fibres. The added glass fibre improves compressive properties by as much as 40% and improves wear resistance greatly. Also the deformation strength under load while leaving substantially unchanged the electrical and chemical characteristics. Fiberglass is the most commonly used filler for PTFE. The disadvantage is that it is much more abrasive for the opposite counter material. Therefore, it is important to remember that glass, has a rather poor resistance against alkalis and is easily attacked by hydrofluoric acid. The coefficient of friction is also slightly increased.
Glass filled PTFE is available in: