Terephthalic Fire-Retardant Gelcoat Resin data sheet (PDF)Ask for a quote
A fire-retardant surface for the terephthalic family
Terephthalic polyesters are built on terephthalic acid, the para isomer of the three phthalic acids. In Samrat Poly Resins’ 2026 catalogue they form the SPR 401 series, and SPR 401 FRGC gives that series its own fire-retardant gelcoat.
It is listed for fire-retardant gelcoat surfaces on rail and transport composite components, automotive composite components and fire-retardant moulded FRP parts — the outer skin of parts where a fire requirement applies.
High thixotropy, and why it helps
The catalogue gives SPR 401 FRGC a thixotropic index of 4.5–6.0, from viscosities of 12,000–18,000 cPs at 2 rpm and 2,000–3,500 cPs at 20 rpm. In practice that is a gelcoat that thins markedly as it is sprayed or brushed and stiffens again on the mould.
For a moulder, the benefit is film build. Gelcoat has to go on at a consistent thickness, including on vertical and return faces, and sag leaves thin spots at the top and heavy runs below. A strongly thixotropic gelcoat holds its film where it is placed.
Colour is part of the specification
SPR 401 FRGC is supplied as an opaque, thick pigmented liquid in white, grey or a custom colour. Because the gelcoat is the tested surface, the colour chosen is part of the construction that goes to fire testing. Agreeing the colour before trials avoids testing one surface and producing another.
Cure and working window
The gelcoat is supplied non-accelerated. At the reference cure — MEKP 1.5% with cobalt octoate 0.4%, each added separately — its typical gel time is 12–22 minutes at 25 °C. Density is 1.25–1.45 g/cm³ and styrene 28–35% by weight.
Fire performance is proven on the part
As with any fire-retardant gelcoat, no classification is quoted for SPR 401 FRGC itself. Transport standards classify a tested specimen of the finished construction, so the gelcoat, the fire-retardant laminate behind it and the thickness are selected and tested together.