Composites are hybrid materials in which two or more substances with very different physical and chemical properties, are combined to form a new superior material. The constituents remain distinct in the composite, and the combination gives the final material unique qualities which the constituents could not deliver by themselves.

The most popular composite materials are those based on polymers reinforced with glass fibres (fibreglass) or carbon fibres. However, there are also composites based on particle-reinforcements, metal matrices, ceramic matrices, nano-composites, and bio materials.

The potential advantages of composites over more traditional materials include:

	Increased specific stiffness
	Increased specific strength
	Reduced density
	Increased toughness
	Improved ease of processing in high-end applications
	Lower cost in specific markets
	Modified electrical conductivity
	Modified thermal, optical, magnetic behaviour
	Improved corrosion resistance
	Lower gas permeability
	Modified dynamic behaviour

Composite materials can provide significant benefits over traditional materials. However, due to the wide range of combinations of constituents, structural arrangements and processing methods, the design and computer simulation processes are more complex.

The major markets and development of composite materials are in high performance sectors such as aerospace, and high volume markets such as marine, aerospace and automotive. These diverse materials are also of growing importance in a wide range of applications including building and infrastructure, agriculture, health, and increasingly sports and leisure applications.