Prepreg (pronounced pree’ preg) is a type of reinforcement material that’s pre-impregnated with resin and hardener; the curing reaction is active, but has been delayed by low storage temperatures. It uses high-end epoxies, and comes in all fiber types and in many forms including unidirectional, biax, triax, quadrax, and so on.

Though prepreg has a short working time, it has many advantages such as lack of dry spots and/or resin-rich areas, less waste, less mess, and excellent results that are easy to duplicate. It comes ready to use, and doesn’t require additional resin for layup.

But there’s a price for all that convenience because prepreg is very expensive. If you estimate the cost of the resin system and laminants separately, prepreg will usually be more expensive. You also need a place to store it since prepreg must be kept in a freezer at very low temperatures to slow the curing process until you’re ready to use it.

Because the curing process is active, prepreg has a relatively short shelf life compared to traditional reinforcement materials. It varies but is typically about a year, if stored according to the manufacturer’s specifications.

When handling prepreg, it’s important to observe all safety precautions specified by the manufacturer, including adequate ventilation and skin and eye protection.

Return to Wet Layup Guide