The question
A buyer with a storage or process vessel to line usually knows the medium but not the resin. Samrat Poly Resins has three candidates for this kind of service: two isophthalic grades from the 2026 catalogue, each listed for a specific service, and a vinyl ester for more corrosive work.
How the three differ
SPR 301 OT and SPR 301 OS are both isophthalic unsaturated polyesters. They differ in the services they are catalogued for — OT for oil-storage-tank lining and chemical equipment, OS for organic-solvent storage, sewage pipes and effluent-treatment equipment — and in their typical liquid values. OS is non-thixotropic and a little thinner.
Vinyl Ester Resin is a different family: a Bisphenol-A epoxy vinyl ester. Vinyl esters have fewer ester links along the chain than polyesters, which is why they are chosen for FRP facing corrosive or chemical service.
Published typical values
None of these figures is chemical-resistance data. They describe the liquid resins, and show that the three are processed similarly — all cure at room temperature with MEKP — so the choice is about service, not workshop practice.
| Property | Oil Storage Tank Grade Resin (SPR 301 OT) | Organic Solvent-Resistant Grade Resin (SPR 301 OS) | Vinyl Ester Resin (SPR 501 VE) |
|---|---|---|---|
| Chemistry | Isophthalic unsaturated polyester | Isophthalic unsaturated polyester | Bisphenol-A Epoxy Vinyl Ester |
| Viscosity (typical) | 300–600 cPs at 25 °C | 200–400 cPs at 25 °C | 350 cPs (at 25°C) |
| Gel time / pot life (typical) | 15–35 minutes at 25 °C | 15–35 minutes at 25 °C | 15–20 minutes at 25°C (see TDS test condition) |
| Specific gravity / density (typical) | 1.04–1.14 | 1.03–1.15 | 1.05 g/cm³ |
| Styrene content (typical) | 33–45% by weight | 35–50% by weight | 40% |
| Source of values | 2026 catalogue; grade TDS | 2026 catalogue; grade TDS | Vinyl Ester 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 none of them is
None has a published chemical-compatibility chart, and none is suitable for every chemical. Isophthalic chemistry improves resistance compared with orthophthalic grades; vinyl ester goes further for many media. The medium, its concentration and temperature, the contact type and the laminate construction — especially the corrosion barrier — decide suitability in every case.