BMC Compound
BMC (Bulk Molding Compound) is a dough-like thermoset material — resin, chopped glass fiber and mineral filler pre-mixed by weight — built for parts that need electrical insulation, flame retardance and complex geometry in one shot.
Susdura is a factory-direct BMC material manufacturer in Ningbo, China. Since 1994, we've supplied custom bulk molding compound to buyers across 40+ countries, in general-purpose, flame-retardant, low-shrink and high-strength grades.
BMC — Bulk Molding Compound Material
BMC (Bulk Molding Compound), also written bulk moulding compound and sometimes called dough molding compound, is a ready-to-mold BMC thermoset plastic material. Unlike SMC's sheet form, BMC is mixed and supplied as a dough-like mass — a blend of unsaturated polyester resin, chopped glass fiber, mineral filler, initiators and pigments, pre-dosed by weight rather than cut from a roll.
Compared with SMC, this BMC plastic material carries a higher filler content and shorter glass fiber, which trades some mechanical strength for better flow into complex, thick-walled or thin-ribbed cavities. BMC is generally the choice when a part's geometry is more intricate than its structural load is demanding.
Higher filler, shorter fiber, dough-like bulk form — flows into complex, thick-section parts. SMC runs the opposite trade: longer fiber, sheet form, better suited to large, thin, high-strength panels.
What Goes Into a BMC Compound
Three main ingredients, pre-dosed by weight and blended into a dough-like mass rather than a sheet.
Unsaturated Polyester Resin
Binds the compound together and gives the cured part its rigidity and chemical resistance.
Chopped Glass Fiber
Shorter fibers, roughly 6–13mm, chosen for flow into fine, complex cavities.
Mineral Fillers
Calcium carbonate and similar fillers, at a higher loading than SMC, control cost, shrinkage and flame behavior.
The BMC Molding Compound Process
A batch premixing process turns raw resin, filler and fiber into a dough-like BMC compound, ready for either molding method below.
Resin Paste Mixing
Resin, initiator, pigment and mold release agent are blended into a base paste.
Filler Addition
Mineral filler is folded in at high loading to build the bulk of the compound.
Fiber Blending
Short glass fiber is mixed in at reduced speed to avoid breaking the strands.
Thickening & Aging
The dough-like mass thickens to molding viscosity before it's ready to be molded.
BMC compression molding presses a charge of compound in a heated matched-metal mold — the standard route for thicker, larger parts.
BMC injection molding feeds the dough-like compound through a screw into the cavity — suited to higher-volume runs with finer detail.
Why Manufacturers Choose BMC
The higher filler loading and shorter fiber of this BMC polymer give it excellent flow, filling intricate, thick-section cavities that would be difficult for a sheet-form material — while the polyester BMC resin base still delivers strong electrical insulation.
- Glass fiber content10% – 20%
- Glass fiber length6mm – 13mm
- Molding temperature140°C – 165°C
- Molding processCompression & Injection
- Dielectric propertiesStrong insulator
Industries Built on BMC Compound
This BMC composite's flow into complex shapes and electrical insulation make it a common choice across these fields.
Electrical & Electronics
When a breaker housing or switchgear part has to survive an arc fault without tracking or burning through, engineers reach for BMC over general-purpose plastics — it's why it's still the default for terminal blocks after decades in the field.
Automotive
Ignition coil covers and under-hood brackets sit close to heat and constant vibration — BMC holds its shape and insulation there long after standard thermoplastics would sag or crack.
Home Appliances
Cistern fittings and handles that get opened and closed thousands of times still need to look and fit right on day one of year five — BMC's dimensional stability is what makes that possible at scale.
Industrial Equipment
Pump housings and valve bodies facing chemical exposure are a classic case where metal corrodes and standard plastics soften — BMC is the common swap-in that just keeps running.
Not sure BMC fits your industry? Send us your part drawing and we'll tell you within 24 hours — no obligation.
BMC Grades We Supply
The right formulation is matched to your part's electrical, thermal and mechanical requirements.
Standard BMC
Balanced strength, insulation and cost for everyday enclosures and structural parts.
FR-Grade BMC
Meets flammability requirements for switchgear and electrical enclosures.
Low-Shrink BMC
Tighter dimensional control for parts with fine surface finish or fitment requirements.
Reinforced BMC
Higher glass-fiber loading for structural, load-bearing components.
Company Overview
35 years of thermoset composite manufacturing experience · A dedicated BMC material production platform
China's Leading BMC Material Brand
SUSDURA was founded in August 1990 by Mr. Dibo Xu, and today operates a dedicated BMC production base in Wenzhou, running 20 semi-automatic BMC production units with separate color-controlled production management to reduce cross-color contamination and keep batch-to-batch consistency high.
Our engineering team develops custom BMC formulations around electrical insulation, flame retardance, weather resistance, chemical resistance and mechanical strength — supported by an in-house laboratory for material testing and validation, so customers can verify performance before moving into mold trials and mass production. With BMC production capacity of up to 50,000 tons per year and a delivery lead time within 5 days for repeat orders up to 10 tons, SUSDURA is built to support both new BMC part development and stable high-volume manufacturing.
Common Questions
What's the difference between BMC and SMC compound?
BMC is a dough-like bulk material with shorter fiber and more filler, best for complex, thick-section parts; SMC is a sheet material with longer fiber, better suited to large, thin-walled panels.
Is BMC suitable for injection molding?
Yes — BMC bulk molding compound flows well enough to be processed by either compression molding or injection molding, unlike SMC which is compression-only.
How is BMC's flame resistance rated?
Flame-retardant BMC grades are formulated to meet standard flammability classifications for electrical enclosures — the exact rating depends on the grade selected.
Can BMC replace metal parts?
In many electrical and appliance applications, yes — BMC's insulation, corrosion resistance and lighter weight make it a common metal replacement where extreme structural load isn't the main requirement.