Dough moulding compound in brief
DMC — also called BMC, bulk moulding compound — is made in a batch mixer rather than on a sheet line. Resin, filler, initiator, release agent and other ingredients are blended into a paste, then short chopped glass fibres are folded in until the mix becomes a stiff, dough-like mass.
The dough is weighed into charges and moulded under heat and pressure, most often by compression moulding, and in some shops by transfer or injection moulding. It suits compact parts with ribs, bosses and inserts: electrical housings, switchgear parts, fittings and small structural components.
How DMC differs from SMC
Both are hot-moulded polyester compounds, but they are made and used differently. SMC is a sheet with longer chopped glass, cut and stacked into large, relatively thin tools. DMC is a bulk dough with shorter fibre, pressed into compact, often intricate parts. The existing DMC versus SMC guide covers the distinction in detail.
Where SPR 301 DMC fits
SPR 301 DMC is the isophthalic resin the 2026 catalogue lists for dough moulding compound production and compression-moulded composite components. In the catalogue’s combined SMC / DMC entry it shares its typical specification with SPR 301 SMC — viscosity 800–1,400 cPs at 25 °C, gel time 12–18 minutes at 25 °C, specific gravity 1.10–1.14, styrene 31–36% by weight — but it is listed as its own product for the dough form.
The catalogue also offers orthophthalic and terephthalic DMC resins, and chooses among them by the chemistry the compound needs.
What the compounder decides
Filler type and loading, fibre length and content, initiator, release agent and moulding conditions are the compounder’s formulation. Electrical, mechanical and flammability performance belong to that formulated, moulded compound and its testing. The resin’s role is to suit the formulation, and the choice of family should follow what the moulded part requires.