Definition
A composite reinforcement fabric (such as fiberglass, carbon fiber, or aramid cloth) that has already been saturated with a controlled amount of uncured resin by the manufacturer. It is supplied frozen or refrigerated to slow the curing reaction, and is later laid into a mold and cured with heat and pressure to form a finished composite part.
Plain English
Cloth that already has the glue mixed into it, kept cold so it stays workable, then heated later to harden into a strong part.
Context Anchor
Seen in composite aircraft construction and repair, especially when maintenance instructions call for specific storage, handling, layup, and curing procedures.
Derivation
Short for preimpregnated. The prefix pre- means before, and impregnated means soaked through. So prepreg literally means soaked through ahead of time — the resin is already in the fabric before the technician receives it.
Why Pilots Care
Prepreg parts have very precise resin-to-fabric ratios, which gives consistent strength and weight. Repairs must use approved materials and cure procedures or the structure will not regain its rated strength.
Grounding Statement
Picture a roll of aircraft fabric kept cold and protected, already tacky with the material that will harden when the repair is cured.
Intuition Check
Prepreg is not just dry fabric waiting for resin to be added. The resin is already in the fabric in a controlled amount.
Example Sentence 1
The technician removed the prepreg from the freezer and let it warm to room temperature before laying it into the mold.
Example Sentence 2
Prepreg sheets must stay in the freezer until they are needed for the repair.