Unsaturated polyester resins: Characteristics
Gel time and viscosity: what a fabricator checks
What this tab covers The physical and chemical properties that set its grade, price and uses, with the commercial grades and the standards that define them.Fabricators choose UPR on viscosity, gel time, styrene content, heat deflection temperature and chemical resistance. These decide how fast a part can be laid up and cured and whether it survives water, acids or heat in service.
Properties that matter commercially
| Property | Value / specification | Why it matters | Source |
|---|---|---|---|
| Styrene content | about 30-45% (indicative) | Sets viscosity, cure and emissions | indicative |
| Viscosity at 25 C | about 300-1,500 mPa s (indicative) | Wet-out of glass fibre | indicative |
| Gel time | about 10-30 minutes with standard MEKP and cobalt (indicative) | Working time for lay-up | indicative |
| Heat deflection temperature | about 60-120 C depending on type (indicative) | Service temperature | indicative |
Commercial grades
- General-purpose orthophthalic laminating resin
- Isophthalic and NPG-isophthalic (pipes, tanks, gelcoats)
- DCPD resins (marine, low emission)
- SMC/BMC resins
- Artificial stone and casting resins
- Fire-retardant resins
- Recycled-PET-based resins