SMC
GB GB/T 25054
SMC is a sheet moulding compound of chopped glass fiber, unsaturated polyester resin, filler and catalyst, supplied as ready-to-mould sheet for matched-metal compression moulding and specified in the GB/T 25054 family.
Reference datasheet — SMC is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
SMC grades and fills
SMC is supplied in 6 conditions, soft to hard.
Compare all 6 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Low-density SMC with hollow glass microspheres | Use where mass reduction of 25–35 % versus standard SMC matters more than peak stiffness (vehicle closures, truck panels). | 55 | 1.3 | 87 Shore D | |
Low-profile Class A surface SMC | Choose when the molded part must be primed and painted to a Class A automotive finish with near-zero shrinkage. | 65 | 1.2 | 90 Shore D | |
Flame-retardant / electrical grade SMC | Pick for switchgear, busbar supports, meter boxes and insulating parts needing V-0, high CTI and glow-wire performance. | 65 | 1.2 | 90 Shore D | |
Vinyl-ester matrix SMC | Choose for chemical plant covers, flue components and hot-water contact where standard polyester SMC hydrolyzes. | 85 | 1.7 | 90 Shore D | |
HS/HMC | Select for load-bearing brackets, bumper beams and structural reinforcements where SMC must approach laminate stiffness. | 180 | 1.8 | 92 Shore D | |
CF-SMC | Use where the highest specific stiffness in a compression-moldable thermoset is required (motorsport, aerospace brackets). | 250 | 1 | 92 Shore D |
Supply forms, finishes and certifications
Ways SMC is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
PW | Potable-water tank panel grade SMC | Certification |
UV | Weatherable / gel-coated exterior SMC | Grade option |
GPDefault | General-purpose SMC, ~25–30 % chopped glass | Standard supply |
What is SMC?
SMC is a sheet moulding compound of chopped glass fiber, unsaturated polyester resin, filler and catalyst, supplied as ready-to-mould sheet for matched-metal compression moulding and specified in the GB/T 25054 family. It is used for large, stiff, dimensionally stable and electrically insulating mouldings at moderate tooling cost, with 75 MPa tensile strength, 1.85 g/cm³ density and 130 °C service. As a thermoset it cannot be welded or reprocessed, elongation is only 1.5%, and the glass content makes trimming abrasive. Vinyl ester versions raise chemical resistance where polyester is marginal. SMC has a density of 1.85 g/cm³ (0.0668 lb/in³), heavier than 96% of polymer grades. Its glass-transition temperature is 115°C (239 °F). SMC has a tensile strength of 75 MPa (10.9 ksi), stronger than 80% of polymer grades. Elongation at break is 1.5% and the elastic modulus is 11 GPa (1.6 Msi).
What is SMC used for?
- electrical switchgear housings
- automotive body panels
- bathroom fixtures
- junction boxes
Advantages
- Low, predictable mold shrinkage — 0.1%, better than 99% of polymer grades
- Stiff — 11 GPa (1.6 Msi), better than 97% of polymer grades
- Low embodied carbon — 3.2 kg CO₂/kg, better than 81% of polymer grades
- Good UV / weathering resistance — 55/100, better than 77% of polymer grades
Limitations
- Limited ductility — 1.5%, worse than 98% of polymer grades
- Heavy — 1.85 g/cm³ (0.0668 lb/in³), worse than 96% of polymer grades
- Limited formability — 5/100, worse than 95% of polymer grades
- Difficult to weld — 5/100, worse than 89% of polymer grades
- Difficult to machine — 30/100, worse than 87% of polymer grades
SMC properties
Typical room-temperature values; bars are the position among polymer grades.
Physical4
SMC has a density of 1.85 g/cm³ (0.0668 lb/in³), heavier than 96% of polymer grades. Its glass-transition temperature is 115°C (239 °F).
Mechanical12
SMC has a tensile strength of 75 MPa (10.9 ksi), stronger than 80% of polymer grades. Elongation at break is 1.5% and the elastic modulus is 11 GPa (1.6 Msi).
Thermal10
SMC is rated for continuous service to 130°C (266 °F). It conducts heat at 0.25 W/m·K (0.144 BTU/hr·ft·°F), better than 72% of polymer grades. Thermal expansion is 25 µm/m·K (13.9 µin/in·°F).
Electrical7
SMC is an electrical insulator with a dielectric strength of 15 kV/mm (381 V/mil) and a resistivity of 1×10¹¹ Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (70/100), worse than 78% of polymer grades. UV resistance is good.
Sustainability4
Producing a kilogram of SMC takes about 60 MJ of energy and emits 3.2 kg of CO₂ — less than 96% of polymer grades. Typical recycled content is 0%.
Manufacturability6
SMC's machinability is poor (30/100, worse than 87% of polymer grades); weldability not recommended (5/100); formability not recommended (5/100).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the polymer family
Yield strength against density for every polymer grade FabDigit runs. SMC is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SMC
Is SMC easy to machine?
Highly abrasive — drill and trim with PCD or diamond-coated tooling at high speed/low feed, back the part to avoid edge chipping, and extract glass dust.
Can SMC be welded?
Thermoset — cannot be welded; join by structural adhesive (urethane/epoxy), molded-in inserts, bolts or rivets.
Can SMC be formed, bent or molded?
Compression mold matched-metal at 140–160 °C, 5–15 MPa, ~30–45 s/mm wall; charge 40–70 % of cavity area and keep flow paths short to control fiber orientation and knit lines.
SMC chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| unsaturated polyester resin (styrene-croorthophthalic/isophthalic UP; vinyl ester in VE grade | 20 – 32 | 26 |
| glass fiber (chopped, 12–50 mm)45–65 % in HS/HMC grades | 20 – 35 | 28 |
| low-profile additive (thermoplastic, PS/controls cure shrinkage / Class A surface | 2 – 6 | 4 |
| zinc stearate / internal mold release | 2 – 5 | 3.5 |
| MgO or Mg(OH)2 thickenerB-stage maturation | 0.5 – 1.5 | 1 |
| peroxide initiator (TBPB/TBPO) | 0.5 – 1.5 | 1 |
| pigment / additives | 0.5 – 3 | 1.5 |
| calcium carbonate fillerreplaced wholly/partly by ATH in FR grades | ≥ 30 (balance) |
What surface finishes work on SMC?
In-mold coating or primer-surfacer plus 2K polyurethane paint for Class A; deflash edges, degrease and lightly abrade before bonding or painting; no plating without special conductive pretreatment.
Equivalent designations
Standards and trade names that resolve to SMC in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- GB (China)
- GB/T 25054
How much does SMC cost?
SMC is a standard-cost polymer ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SMC — frequently asked
What is SMC used for?
SMC is typically used for electrical switchgear housings, automotive body panels, bathroom fixtures and junction boxes. In short: low-cost structural thermoset; good high-voltage insulation; not weldable or recyclable.
What is the tensile strength of SMC?
SMC has a typical tensile strength of 75 MPa (10.9 ksi) — stronger than 80% of polymer grades. Strength varies by condition: see the 6 listed tempers.
Is SMC easy to machine?
Not especially — machinability is rated poor (30/100, worse than 87% of polymer grades). Highly abrasive — drill and trim with PCD or diamond-coated tooling at high speed/low feed, back the part to avoid edge chipping, and extract glass dust.
Can SMC be welded?
Not readily — weldability is rated not recommended (5/100). Thermoset — cannot be welded; join by structural adhesive (urethane/epoxy), molded-in inserts, bolts or rivets.
What surface finishes work on SMC?
In-mold coating or primer-surfacer plus 2K polyurethane paint for Class A; deflash edges, degrease and lightly abrade before bonding or painting; no plating without special conductive pretreatment.
Can SMC be formed, bent or molded?
Compression mold matched-metal at 140–160 °C, 5–15 MPa, ~30–45 s/mm wall; charge 40–70 % of cavity area and keep flow paths short to control fiber orientation and knit lines.
What is the maximum service temperature of SMC?
SMC is rated for continuous use to about 130°C (266 °F), and briefly to 180°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does SMC cost?
SMC is a standard-cost polymer ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- GB/T 15568 (SMC) — SAC (2008)
- ISO 527-4 / ISO 14125 — tensile and flexural properties of fiber-reinforced plastic composites — ISO (1998)
- Engineered Materials Handbook Vol. 2: Composites — ASM International (1987)
- SMC compound technical datasheets (Menzolit, Polynt Composites, IDI Composites, Continental Structural Plastics) — various (2023)
- UL Yellow Card / IEC 60112 CTI and UL 94 listings for polyester molding compounds — UL Solutions (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.