Quick facts
- Grades compared
- SPR 201 GPC · SPR 301 · SPR 401 TL
- Tooling chemistry
- Isophthalic NPG-based, in the SPR 401 code range — not terephthalic
- Tooling supply
- Non-accelerated · moderately thixotropic
- Decided by
- Whether you are building the part or the mould it is made on
What differs: a resin for the part, a resin for the mould
GP Clear Resin, Lamination Resin and ISO Polyester Resin are laminating resins for the part itself. GP Clear Resin is the standard orthophthalic general-purpose grade; Lamination Resin (LR Resin) is a transparent unsaturated polyester listed for door-skin, plywood and FRP bonding, with published values of 400 cPs, a 5-minute gel time and 35% styrene; ISO Polyester Resin is the general isophthalic grade for water and chemical service.
SPR 401 TL is listed for a different job: composite mould production and tooling and die preparation. The catalogue describes it as a highly reactive, high-molecular-weight isophthalic NPG (neopentyl glycol)-based polyester. It is kept in the SPR 401 code range but it is not a terephthalic resin. It is supplied moderately thixotropic — 400–650 cPs at 60 rpm rising to 1,500–2,500 cPs at 6 rpm — so it thins while being worked and holds better at rest.
How to decide
Ask first what you are making. If it is the product — a tank, a panel, a door skin — choose among the laminating resins by service: GP Clear Resin for general work, Lamination Resin for door and plywood bonding, ISO Polyester Resin where the part faces water or chemical service. If it is the mould that products will be pulled from, SPR 401 TL is the grade the catalogue lists for mould production.
Then check the working conditions. SPR 401 TL’s moderate thixotropy suits building up a laminate on the vertical faces of a pattern, and its 15–30 minute gel time at 25 °C sets the pace of that build-up. Many workshops build moulds from a general laminating resin; if yours does, the decision to change is a trial on your own pattern, not a rule.
What the data does not tell you
The catalogue does not publish a heat distortion figure, shrinkage, surface-finish rating or number of pulls for SPR 401 TL, and none is claimed here. A mould’s life and finish also depend on the mould-face surface layer, the laminate build-up, post-cure and release practice. The ISO Polyester Resin TDS figures describe that resin, not a mould made from it.
Sources, roles and the Nepal enquiry path
GP Clear Resin, Lamination Resin and ISO Polyester Resin values are from their supplier Technical Data Sheets as recorded on this site. SPR 401 TL values are the typical specification in the supplier’s 2026 product catalogue; no Technical Data Sheet for that grade has been published 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.
General laminating resins vs SPR 401 TL: decision table
| Criterion | GP Clear Resin (SPR 201 GPC) | ISO Polyester Resin (SPR 301) | Tooling Grade Resin (SPR 401 TL) |
|---|---|---|---|
| Chemistry | Orthophthalic unsaturated polyester | Isophthalic unsaturated polyester | Isophthalic NPG-based polyester (not terephthalic) |
| Supply condition | Non-accelerated; thixotropy not stated | Non-accelerated; thixotropy not stated | Non-accelerated · moderately thixotropic (index 2.5–3.8) |
| Viscosity | 350–450 cPs | 500 cPs at 25 °C | 400–650 cPs at 60 rpm; 1,500–2,500 cPs at 6 rpm |
| Gel time | Under 8 minutes | 15 minutes at 25 °C | 15–30 minutes at 25 °C |
| Styrene content | 33–40% | 40% by weight | 35–42% by weight |
| Reference cure | MEKP + cobalt octoate, dosed per the TDS | MEKP catalyst with cobalt octoate accelerator, per the TDS | MEKP 1.5% + cobalt octoate 0.4%, added separately |
| Listed uses | Hand lay-up, spray-up, moulding, FRP water tanks, sheets, panels | Chemical storage tanks, FRP pipes, process equipment, marine parts, corrosion service | Composite mould production; tooling and die preparation |
| Choose when… | You are laminating the part itself for general service | You are laminating a part for water or chemical service | You are building the mould or tool that parts are made on |
Sources: GP Clear Resin (SPR-TDS-GCR) and ISO Polyester Resin (SPR-TDS-IPR) values from their supplier Technical Data Sheets as recorded on this site; SPR 401 TL values from the supplier’s 2026 product catalogue. Typical values describe a grade; they are not batch guarantees or acceptance limits.
Frequently asked questions
Is SPR 401 TL a terephthalic resin?
No. It is an isophthalic NPG-based resin that is kept in the SPR 401 code range.
Can I make a mould with GP Clear Resin?
GP Clear Resin is listed for general lay-up and moulding, not specifically for tooling. SPR 401 TL is the grade the catalogue lists for mould production; compare them on a trial.
What does “moderately thixotropic” mean in practice?
The resin is thinner while it is being worked and thicker at rest, which helps it hold on vertical faces. The catalogue lists a thixotropic index of 2.5–3.8.
Does “ISO” in ISO Polyester Resin mean a certification?
No. “ISO” means isophthalic, the chemistry of the resin.