Both wind turbine blades and ship parts made out of composite materials require plugs in their construction process.

A plug for a composite mold is typically a representation of the finished part, usually a mock up of a part.

In planning for the mold certain factors must be taken into consideration; material, surface finish, draft angles, undercuts, and method of production.

Plugs made from scratch can be done from a wide variety of materials using a wide variety of methods. For instabce a foam core for the body, mounted on plywood to make the flange, and glassed over it to provide a stable surface to fair over. Other possibilities are MDF, high density foam, styrofoam, body filler, and other materials. For large parts often a framework is built and then layered with foam, fiberglass, and body filler before priming and finishing.

The surface quality of your plug and your backing board will be reflected in the gelcoat of the mold. Thus it is really important to bring the surface finish up to the level desired in the finished composite part.