Different reinforcements, different resins
GP Clear Resin (SPR 201 GPC) is the general orthophthalic laminating grade for glass-fibre work. SPR 301 LV is a low-viscosity isophthalic grade designed to impregnate jute. The reinforcement is usually what decides between them.
Published typical values
| Property | GP Clear Resin (SPR 201 GPC) | Low-Viscosity Isophthalic Resin (SPR 301 LV) |
|---|---|---|
| Chemistry | Orthophthalic, Unsaturated Polyester | Isophthalic unsaturated polyester |
| Appearance | Clear | Clear, water-white to light-straw liquid |
| Viscosity (typical) | 350–450 cPs | 80–180 cPs at 25 °C |
| Gel time / pot life (typical) | < 8 minutes | 40–90+ minutes at 25 °C |
| Styrene content (typical) | 33–40% | 42–50% by weight |
| Reference cure | MEKP 1.5% + cobalt octoate 0.4% | MEKP 1.5% + Cobalt Octoate 0.2% — added separately during use |
| Source of values | GP Clear Resin 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.
Why lower viscosity is not simply better
A thinner resin penetrates thick, absorbent reinforcement more easily, which is why LV suits jute. On glass mat, though, a very thin resin can drain from vertical faces, and more styrene — LV is 42–50% by weight typical — means more to manage in ventilation. GP Clear’s 350–450 cPs is set for glass-fibre lay-up.
Working time and cure
The two grades have very different working windows at their reference cures: GP Clear gels in under 8 minutes typical, LV in 40–90+ minutes at 25 °C. LV is also referenced with half the cobalt octoate — 0.2% against 0.4% — each added separately with MEKP 1.5%.