Choosing materials for the matrix

For the matrix, many modern composites use thermosetting or thermosoftening plastics (also called resins). The use of plastics in the matrix explains the name 'reinforced plastics' commonly given to composites. The plastics are polymers that hold the reinforcement together and help to determine the physical properties of the end product.

Thermosetting plastics are liquid when being prepared but hardenand become rigid (i.e., they cure) when they are heated. The setting process is irreversible, so that these materials do not become soft under high temperatures. 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 specialized purposes. For example, ceramics is used when the material is going to be exposed to high temperatures (e.g., heat exchangers) and carbon is used for products exposed to friction and wear (e.g., bearings and gears).