Definition
A composite material in which the reinforcing fabric or fiber has already been saturated with a measured amount of uncured resin by the manufacturer. The resin is partially advanced and kept stable by refrigeration until the material is laid up and cured under heat and pressure.
Plain English
Cloth or fiber that comes from the factory already soaked with the right amount of glue-like resin, ready to be shaped and baked solid. It is kept cold so the resin does not harden until you want it to.
Context Anchor
Seen in composite aircraft structure manufacturing and composite repair procedures, especially when a maintenance manual specifies stored material, layup steps, and cure conditions.
Derivation
Short for 'pre-impregnated.' 'Impregnate' comes from Latin roots meaning 'to fill thoroughly.' The name simply tells you the fabric has already been filled with resin before it reaches the technician.
Why Pilots Care
Consistent resin-to-fiber ratio produces stronger, lighter, and more reliable structural repairs that directly affect airframe integrity and flight safety.
Analogy
Think of it like refrigerated cookie dough that already has the right ratio of ingredients mixed in. You shape it, put it in a hot oven, and it sets. Leave it out too long beforehand and it goes bad.
Intuition Check
Prepreg does not mean the part is already finished or strong. It means the fiber material already contains resin and still needs the correct curing process.
Example Sentence 1
The technician removed the prepreg from the freezer and let it thaw in its sealed bag before laying it into the mold.
Example Sentence 2
After the prepreg layers were in place, vacuum bagging and heat were applied to cure the repair.