These plastics also resist wear and attack by chemicals making them very durable, even when exposed to extreme environments. Thermosoftening plastics, as the name implies, are hard at low temperatures but soften when they are heated. Although they are less commonly used than thermosetting plastics they do have some advantages, such as greater fracture toughness, long shelf life of the raw material, capacity for recycling and a cleaner, safer workplace because organic solvents are not needed for the hardening process. Ceramics, carbon and metals are used as the matrix for some highly specialised purposes. Although glass fibres are by far the most common reinforcement, many advanced composites now use fine fibres of pure carbon.
Carbon fibres are much stronger than glass fibres, but are also more expensive to produce.
Carbon fibre composites are light as well as strong. Polymers are not only used for the matrix, they also make a good reinforcement material in composites. For example, Kevlar is a polymer fibre that is immensely strong and adds toughness to a composite. Choosing the manufacturing process Making an object from a composite material usually involves some form of mould. The reinforcing material is first placed in the mould and then semi-liquid matrix material is sprayed or pumped in to form the object.