BMC compression

Bulk Molding Compound


Bulk Molding Compound (BMC) is a semi-finished product made from catalyzed unsaturated polyester resin blender, various fillers and additives, reinforced by chopped glass fibers (20%) which is dedicated to large series moulding processes.

The BMC is charged with chopped fibers. The percentage of fiberglass varies from 10 to 30%, their length form 6 to 12 mm.

The BMC is generally injected in a closed cavity (made of a mold and of a backing-mold) at a  regulated in temperature (130 to 150 ° C). the closing of the mold generates the creep in compression of the compound and the compound is forced through an orifice (injection nozzle) into the closed mould.

The very short cure time allows quick stripping of the part.

Advantages of BMC

  • Two smooth faces
  • Possibility of complex shapes
  • High precision molding
  • Moderate material cost
  • High molding speeds
  • Low impact of labor on the quality of parts


  • Large series
  • Small and medium-siezd parts

Raw material

Bought or home-made compound

  • Mostly polyester resins, chemical shim agent, catalysts, inhibitors, mould release agents, pigments…
  • Reinforcement : 6 to 12 mm chopped fiberglass  (reinforcement rate : 20 to 50%)


  • Preparation : weighting devices, compound mixer
  • Moulding : High compression press with adjustable pressing speed, thermo-regulated chrome steeled moulds


  • Automotive (tourism and commercial vehicles), car bodywork, protection covers.
  • Electrical devices
  • Various industrial parts