prepregs

Prepregs, short for pre-impregnated composites, consist of reinforcement fibers—most commonly carbon, glass, or aramid—that are coated with a resin system which has been partially cured (B-stage). The resin content is controlled so the material remains tacky and lay-up friendly, yet stable enough to handle until it is cured into a finished laminate through heat and pressure.

Common matrices include epoxies, cyanate esters, and bismaleimides. Prepregs are manufactured as fabrics, tapes, or tows that are impregnated and partially cured to the prepreg state. Carbon fiber/epoxy prepregs are dominant in high‑performance applications; glass fiber and other fibers are used with various resin systems for lower cost or higher temperature resistance.

Storage and shelf life depend on the resin system and temperature. To slow cure, prepregs are stored refrigerated or frozen, often around -18 to -20 C, with shelf lives ranging from several months to a year or more; some systems offer limited room-temperature storage for brief periods.

Processing typically involves layup on tooling followed by consolidation under vacuum and heat. Curing is performed in an autoclave or in out-of-autoclave processes, depending on the material and manufacturing requirements. Autoclaves apply pressure to reduce voids and improve laminate properties; OOA methods rely on vacuum, heat, and sometimes pressure assist.

Advantages include high fiber content, excellent control of resin distribution, high strength-to-weight ratios, and good surface finishes. Disadvantages include higher cost, limited shelf life, need for controlled storage and handling, and reliance on specialized equipment and processes.

Applications are widespread in aerospace, automotive, wind turbine blades, sporting goods, and marine structures. Ongoing developments aim to extend shelf life, enable lower-cost out-of-autoclave processing, and improve sustainability through recycling and easier manufacturing.