Bulk-molding compound is a premixed material containing resin, filler, glass fibers, and various additives. It is supplied in a doughlike, bulk form and as extruded rope. Complex parts with bosses and ribs are easily molded from SMC-R because it flows readily in a mold. These materials are used for structural, load-bearing components. Because the hardeners or curing agents become part of the finished structure, they are chosen to provide desired properties in the molded part.
Epoxies have outstanding adhesive properties and are widely used in laminated structures.
The cured resins have better resistance than polyesters to solvents and alkalies, but less resistance to acids. Phenolics, the oldest of the thermoset plastics, have excellent insulating properties and resistance to moisture. Chemical resistance is good, except to strong acids and alkalies. Water absorption is low, and dielectric properties are excellent. Glass is the most widely used reinforcing material in thermoset composites.