What is BMC

BMC (Bulk Moulding Compound) is a fibre reinforced compound, in a thermoset resin matrix, with mineral fillers and different additives. Generally thermoset unsaturated polyester or vynil-ester resins are used as organic matrix.

With the aim of enhance its characteristics and improve its transformation, other components are added: catalysts, inhibitors, thermoplastic additives, demoulding agents, thickeners and pigments.


Resins, fillers and additives are automatically weighted and mixed together to form the mother paste. In a second mixer, more fillers, colour pigments and chopped glass fibre are automatically weighted and mixed together within a computer-controlled process to ensure a perfect impregnation or wet out of the glass fibre.

The resulting mix is then sent to an extruder, which compacts the BMC material and packs it into bags. At the end of the process, after BMC bags pass through a metal detector to prevent material from having any metallic foreign object, BMC bags are packed into boxes.

BMC Production Diagram


BMC must mature before it reaches optimal conditions for moulding. Typically the required maturation time is between 2 and 4 days, depending on the specific formulation.

Even after the material has matured, it continues to thicken at a speed dependant on the storage temperature. Therefore there is an optimal utilisation period of typically, between 1 and 6 months, dependant mainly on the specific formulation and storage temperature, which is recommended to be between 15 and 25ºC. Higher storage temperatures can significantly reduce the usability time of BMC.


BMC can be moulded both in injection or compression processes for large scale production of medium-size or small complex parts. Although moulding activities are carried out by our customers, Astar assists during moulding trials and offers complete technical assistance everytime is required.

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