Two chemistries under one name
“Clear casting resin” is sold in two chemistries that behave very differently. SPR 201 CC is an orthophthalic unsaturated polyester cured with a small dose of MEKP initiator and cobalt accelerator, each added separately. The epoxy Clear Casting Resin is a two-part system mixed with its hardener at a fixed 2:1 ratio by weight.
Neither is an upgrade of the other. They suit different articles and different workshops.
Published typical values
A polyester gel time and an epoxy pot life measure different things; they are shown together for orientation only.
| Property | SPR 201 CC Clear Casting Resin | Clear Casting Resin |
|---|---|---|
| Chemistry | Orthophthalic unsaturated polyester | Epoxy, Two-Part System |
| Appearance | Clear liquid | Clear |
| Viscosity (typical) | 350–450 cPs | 900 cPs (at 25°C) |
| Gel time / pot life (typical) | Under 8 minutes | Pot life 40 minutes (at 25°C) |
| Reference cure | MEKP 1.5% + Cobalt Octoate 0.4% — added separately during use | Resin and hardener, 2:1 (Resin : Hardener, by weight) |
| Source of values | 2026 catalogue; grade TDS | Clear Casting Resin 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.
What the published data says
The epoxy Clear Casting Resin publishes a maximum casting depth of 30 mm per pour, shrinkage below 0.2% and full cure in 72 hours at 25 °C — figures that suit deep, clear, carefully timed pours. SPR 201 CC publishes liquid-resin values only: 350–450 cPs viscosity and gel time under 8 minutes at its reference cure. Polyesters shrink more than epoxies as they cure, and they cure faster, which suits decorative production castings and top coats more than deep clear blocks.
Workshop considerations
Polyester castings release styrene vapour and need good ventilation. Epoxy systems need accurate weighing of resin and hardener, and a mis-measured mix does not cure properly. Both generate heat as they cure, and both need trials at the real article size.