Quick facts
- Grades compared
- DMC/SMC Resin (SPR 201) · SPR 301 SMC · SPR 401 SMC
- Chemistries
- Orthophthalic · isophthalic · terephthalic
- Shared ambient gel time
- 12–18 minutes at 25 °C for all three
- Deciding factor
- Heat, chemical and impact demands on the moulded part
What differs
All three are non-accelerated resins for sheet moulding compound and share the same 12–18 minute ambient gel time at 25 °C. What separates them is the acid the polyester is built on and what the supplier lists for each. DMC/SMC Resin is the orthophthalic grade, published as one resin for both DMC and SMC contexts. SPR 301 SMC is isophthalic and is described as having superior properties to the orthophthalic SMC grade. SPR 401 SMC is terephthalic and is listed with high heat resistance, resistance to corrosive chemicals and strong mechanical and impact properties.
The isophthalic and terephthalic grades also publish higher viscosity ranges than the orthophthalic resin, which matters for filler loading and impregnation of the glass in the compound line.
How to decide
Choose by the finished part, then by the compound. For general-purpose SMC parts where the formulation is already built around an orthophthalic resin, DMC/SMC Resin is the documented route. If the compound is specified with an isophthalic resin, or the catalogue’s description of superior properties compared with the SPR 201 SMC grade is the reason for the change, review SPR 301 SMC. The catalogue publishes no comparative figures behind that wording, so confirm the difference that matters to your part by trial. If the part’s specification calls out heat, corrosive chemicals or impact, review SPR 401 SMC.
A change of resin chemistry changes the compound: filler, thickener, glass content and press conditions may all need to be re-balanced. Plan a compound trial and a moulding trial before switching grades in production.
What the data does not tell you
The gel times are ambient quality-control figures at 25 °C; hot-press cure times depend on your mould temperature, pressure and compound, and are not published. “Superior properties”, “high heat resistance” and “strong impact properties” are catalogue wording without published figures, so they cannot be converted into a heat-deflection or impact value for a finished part.
The orthophthalic values come from a TDS and the other two from the 2026 catalogue; treat small differences as indicative and confirm current documents before ordering.
Sources, roles and the Nepal enquiry path
SPR 301 SMC and SPR 401 SMC values are the typical specification printed in the supplier’s 2026 product catalogue; no Technical Data Sheet for either has been published on this site. DMC/SMC Resin values are from its Technical Data Sheet as shown on its product page.
Samrat Poly Resins, India manufactures the grade and issues its technical information. Samrat FRP Traders is the Nepal supplier and importer and handles enquiries; price, packaging, lead time and stock in Nepal are confirmed on enquiry.
Three SMC resins side by side
| Criterion | DMC/SMC Resin (SPR 201) | SPR 301 SMC | SPR 401 SMC |
|---|---|---|---|
| Chemistry | Orthophthalic polyester | Isophthalic polyester | Terephthalic polyester |
| Product scope | One published grade for both DMC and SMC contexts | SMC grade; a separate product from SPR 301 DMC, sharing its published specification | SMC grade; a separate product from SPR 401 DMC, with its own specification |
| Viscosity | 600 cPs at 25 °C | 800–1,400 cPs at 25 °C | 800–1,500 cPs at 25 °C |
| Gel time | 12–18 minutes at 25 °C | 12–18 minutes at 25 °C | 12–18 minutes at 25 °C (ambient QC) |
| Styrene · specific gravity | 35% · 1.12 | 31–36% · 1.10–1.14 | 32–38% · 1.11–1.15 |
| Supply and reference cure | Non-accelerated; cure as stated in the supplier TDS | Non-accelerated; MEKP 1.5% + cobalt octoate 0.4%, added separately | Non-accelerated; MEKP 1.5% + cobalt octoate 0.4%, added separately |
| Listed uses and properties | DMC/SMC compounds; electrical housings, manhole covers, automotive panels, water tanks, sanitaryware | SMC production; hot-mould and compression moulding; described as superior in properties to SPR 201 SMC | SMC production; compression-moulded parts; high heat resistance, corrosive-chemical resistance, strong mechanical and impact properties |
| Choose when… | The part is general-purpose and the compound formulation is built around an orthophthalic resin | The compound is specified with an isophthalic resin, or the catalogue’s “superior properties compared with the SPR 201 SMC grade” is the reason for the change | The part faces heat, corrosive chemicals or impact that the specification calls out |
Sources: SPR 301 SMC and SPR 401 SMC — Samrat Poly Resins, India product catalogue, 2026 edition (typical specification); DMC/SMC Resin — its supplier Technical Data Sheet as published on this site. Typical values describe each grade; they are not batch guarantees or acceptance limits.
Frequently asked questions
Is the terephthalic SMC resin the same product as the terephthalic DMC resin?
No. SPR 401 SMC and SPR 401 DMC are separate products, and the DMC grade has its own viscosity, gel time and reference cure.
Why do all three show the same gel time?
Each record publishes 12–18 minutes at 25 °C as an ambient figure. It is a quality-control reference, not the cure time in a heated press.
Can I swap resins without changing the compound?
Assume not. Viscosity and chemistry differ, so filler loading, thickening and press conditions should be re-checked with a compound and moulding trial.
Which grade is strongest?
No mechanical figures are published for any of the three. SPR 401 SMC is described with strong mechanical and impact properties; the finished part has to be tested against its own requirement.