Composite properties are much higher, and continuous fibers are therefore used in most high performance components, be they aerospace structures or sporting goods. Matrix materials are usually some type of plastic, and these composites are often called reinforced plastics . There are other types of matrices, such as metal or ceramic, but plastics are by far the most common. There are also many types of plastics, but a discussion of them is beyond the scope of this week's column. Suffice it to say for now that the two most common plastic matrices are epoxy resins and polyester resins.
Composite materials are available as plies or lamina.
There are other forms, but these are the most important for this discussion. Composite properties are best in the direction of the fibers. Perpendicular, or transverse , to the fibers, the matrix properties dominate because load must be transfered by the matrix every fiber diameter. Because most structures are not loaded in a single direction, even though one direction may dominate, it is necessary to orient fibers in multiple directions. This is accomplished by stacking multiple plies together.