Why the catalogue offers three
SMC is used for parts as different as electrical enclosures, automotive panels, water-tank panels and sanitaryware. A single resin chemistry cannot suit all of them, so the 2026 catalogue offers SMC resins in all three polyester families and states that the family is chosen by the chemistry the compound requires.
The three options
The orthophthalic resin is the DMC/SMC Resin (SPR 201 SMC · DMC), the general-purpose option with a published TDS. SPR 301 SMC is isophthalic, from the family the catalogue specifies for water and chemical service. SPR 401 SMC is terephthalic, which the catalogue describes as having high heat-resistant capacity, good resistance to corrosive chemicals and excellent mechanical and impact properties.
Those are qualitative positions. No numerical moulded-part values are published for any of the three.
Published typical values
All three have the same ambient QC gel-time band; their viscosities differ, which affects paste formulation at a given filler loading.
| Property | DMC/SMC Resin (SPR 201 SMC · DMC) | Isophthalic SMC Resin (SPR 301 SMC) | Terephthalic SMC Resin (SPR 401 SMC) |
|---|---|---|---|
| Chemistry | Orthophthalic unsaturated polyester resin | Isophthalic unsaturated polyester | Terephthalic unsaturated polyester |
| Appearance | Pale Yellow | Clear, pale-yellow to light-amber liquid | Clear to slightly hazy, pale-yellow to light-amber liquid |
| Viscosity (typical) | 600 cPs (at 25°C) | 800–1,400 cPs at 25 °C | 800–1,500 cPs at 25 °C |
| Gel time / pot life (typical) | 12–18 minutes (at 25°C; review current TDS for test context) | 12–18 minutes at 25 °C | 12–18 minutes at 25 °C (ambient QC) |
| Specific gravity / density (typical) | 1.12 g/cm³ | 1.10–1.14 | 1.11–1.15 |
| Styrene content (typical) | 35% | 31–36% by weight | 32–38% by weight |
| Source of values | DMC/SMC Resin TDS | 2026 catalogue; grade TDS | 2026 catalogue; grade TDS |
Typical values, reproduced from each product’s own published data. They describe the liquid resin at its reference condition, not a finished part, and are not guaranteed limits.
How to decide
Start from the moulded part: where it is used, what it faces, what finish it needs and what specification it must meet. Choose the family that fits, then confirm by making and moulding compound. When two families both look possible, moulding specimens from each and testing them against the part requirement settles it.