What is the role of fibers and matrix in composite materials?

In composite materials, fibers (typically carbon, glass, or aramid) provide strength and stiffness in their aligned direction, carrying the primary structural loads. The matrix (usually epoxy resin) bonds fibers together, transfers loads between fibers, protects fibers from environment and damage, and provides out-of-plane properties. The fiber-matrix interface is critical for load transfer. Fiber volume fraction (typically 55-65% for aerospace) affects properties - higher fiber content increases stiffness and strength but reduces damage tolerance. The combination achieves properties neither constituent has alone.