Composite materials are strong and lightweight materials and fabrics used in the aerospace, sports, manufacturing, law enforcement and even medical industries. Known for extreme durability and resistance to structural failure, composite materials range from sturdy fibreglass kayak paddles to the life-saving Kevlar worn by soldiers and SWAT team members. However, to truly qualify as a composite material, each product must conform to a set of properties and functions that govern the category.
All composite materials are made of two or more distinctly different materials woven or processed in a way that combines the materials into a uniform shape and consistency. For instance, mixing gravel with cement and adding water will form concrete, a uniform composite that is made up of two separate materials that are chemically and structurally quite different from one another. Wood, a natural composite material, is composed of thin strands of cellulose fibres compressed with lignin (a naturally occurring organic glue), and is considered a composite material because of the differences in chemical and structural properties between cellulose and lignin.
Another important aspect of composite materials plays upon the fact that the two or more materials in a composite are not only chemically and structurally different, but also that they are combined in such a way that they remain separate from one another. This allows the combination of two material properties to reinforce one another, making composites more reliable and durable than other noncomposite materials. The woven fibres in Kevlar, the strand of cellulose in lignin and even the gravel encased in the cement all retain their individual properties because they are not mixed entirely into the glue, or "matrix" of the composite material.
Because composite materials are not mixed entirely, the reinforcement of one material with another adds to the functionality of composites. Fibreglass, for instance, is a composite that relies on strands of fine glass mixed into a matrix of plastic to produce a safe and sturdy product. Because these materials are not completely mixed, when fibreglass is impacted, the strands of glass act to hold the pieces of plastic together so that the product does not shatter or break apart entirely. This is the property of composites that gives them their strength and reliability even under extremely harsh circumstances (space shuttles are made of composites).
Another property of composite materials lies in their usability. Composites are lightweight and durable because the separate materials within act to reinforce one another (strength) but do not require heavy materials or super solid mixtures (lightweight). Because of this property, composites are used in many application that call for light, strong materials: aeroplanes, surf boards, boat hulls, Kevlar and even surgically replaced human joints are made increasingly usable because of the addition of strong composite materials.