Composite construction uses two materials together, each with different physical or chemical properties, to create material with your desired properties. In rocketry, we usually want strong and lightweight materials. Fiberglass components (made of fiberglass cloth and liquid resin) or carbon fiber components (made of carbon fiber material and liquid resin) are two examples of composite construction. And often fiberglass or carbon fiber are used over less strong materials (balsa wood, foam, honeycomb) to obtain an extremely stong yet lightweight part. Aviation and Aerospace use a lot of composite construction.
Carbon fiber is an extremely strong material that can be used in place of cardboard and fiberglass for building your rocket. But it is more expensive. You can purchase ready made components such as body tubes and nose cones from an increasing number of vendors. But sometimes you will need to form your own parts. You can purchase the fabrics and resin separately. And you will see references to pre-preg material. This is fabric with the resin pre-impregnated into that fabric. It is easier and less messy to use, but is more expensive. The web pages under this page will help you with information about how to use composites as well as sources for ready-made parts and materials to make your own. And there is an excellent Yahoo newgroup on “CompositeRockets“.