Quick facts
- Grades compared
- SPR 301 FW · SPR 401 PT
- Chemistry
- Isophthalic (FW) · terephthalic (PT)
- Cure
- Ambient MEKP + cobalt (FW) · heat-activated peroxide, MEKP 0% and cobalt 0% (PT)
- Decided by
- The process: winding onto a mandrel or pulling through a heated die
What differs: chemistry and, above all, cure
SPR 301 FW is an isophthalic grade listed for filament winding, with high binding properties and high strength. SPR 401 PT is a terephthalic grade listed for continuous pultrusion, with strong mechanical properties. Both are supplied non-accelerated and non-thixotropic, because both processes need a resin that flows freely into the fibre.
The cure is where they part completely. SPR 301 FW cures at workshop temperature with MEKP 1.5% and cobalt octoate approximately 0.4%, added separately, and its 20–60+ minute gel time keeps the bath workable through a winding. SPR 401 PT runs in production on a heat-activated peroxide blend at 1.0–2.0% total, with 0% MEKP and 0% cobalt, and gels in 40–80 seconds in a die at 130–140 °C. Its 15–25 minute ambient gel time is only a quality-control check.
How to decide
The process decides, not a ranking of the resins. If you wind pipes or tanks on a rotating mandrel and cure at ambient temperature, SPR 301 FW is the listed grade. If you pull fibre continuously through a heated die to make profiles and structural sections, SPR 401 PT is the listed grade, and your line needs the heat-activated peroxide system it is designed for — an ambient MEKP-cobalt cure is not its production route.
Where the part will face more aggressive chemical service, the vinyl-ester route applies to both processes: Vinyl Ester Resin (SPR 501 VE) is supplier-listed for filament-winding and pultrusion applications, with published values of 350 cPs, a 15–20 minute gel time, 40% styrene and a specific gravity of 1.05. The chemical, its concentration and the temperature decide whether that step is needed.
What the data does not tell you
Neither grade’s values give a pipe pressure rating, a tank service life or a profile’s load capacity; those belong to the part design, fibre content and testing. The catalogue does not publish a chemical-compatibility list for either grade, nor die settings or line speeds for SPR 401 PT beyond the hot-die gel figure. Confirm the grade on a trial run with your own reinforcement and equipment.
Sources, roles and the Nepal enquiry path
SPR 301 FW and SPR 401 PT values are the typical specification in the supplier’s 2026 product catalogue; no Technical Data Sheet for either grade has been published on this site. Vinyl Ester Resin values are from its supplier Technical Data Sheet as recorded on this site.
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.
SPR 301 FW vs SPR 401 PT: decision table
| Criterion | Filament Winding Grade Resin (SPR 301 FW) | Pultrusion Grade Resin (SPR 401 PT) |
|---|---|---|
| Chemistry | Isophthalic unsaturated polyester | Terephthalic unsaturated polyester |
| Process | Filament winding, cured at ambient temperature | Continuous pultrusion through a heated die |
| Supply condition | Non-accelerated · non-thixotropic | Non-accelerated · non-thixotropic |
| Viscosity | 200–400 cPs at 25 °C | 300–600 cPs at 25 °C |
| Gel time | 20–60+ minutes at 25 °C | Hot die: 40–80 seconds at 130–140 °C; ambient QC: 15–25 minutes at 25 °C |
| Styrene content | 35–45% by weight | 36–42% by weight |
| Reference cure | MEKP 1.5% + cobalt octoate approx. 0.4%, added separately | Heat-activated peroxide blend, 1.0–2.0% total; production MEKP 0%, cobalt 0% |
| Listed uses | Filament-winding processes; filament-wound FRP pipes and tanks | Continuous pultrusion; pultruded FRP profiles and structural sections |
| Choose when… | You wind pipes or tanks on a mandrel and cure at workshop temperature | You pull continuous profiles through a heated die |
Source: the supplier’s 2026 product catalogue for both grades. The ambient gel time of SPR 401 PT is a quality-control figure, not a production cure. Typical values describe a grade; they are not batch guarantees or acceptance limits.
Frequently asked questions
Can SPR 401 PT be cured with MEKP and cobalt?
Its production cure is a heat-activated peroxide blend (1.0–2.0%) with 0% MEKP and 0% cobalt. The ambient gel time is only a quality-control figure.
Can SPR 301 FW be used for pultrusion?
The catalogue lists it for filament winding only. For pultrusion it lists SPR 401 PT; any other use would need its own trial.
Is terephthalic stronger than isophthalic?
The catalogue publishes no mechanical figures that would support a ranking. Each grade is listed for its own process; choose by the process.
When should I look at vinyl ester instead?
When the wound or pultruded part faces more aggressive chemical service. Vinyl Ester Resin is supplier-listed for both processes; the actual service decides.