Shop for GPO-3 Thermoset sheets. GPO-3 thermoset sheet is a glass reinforced thermoset polyester sheet material. GPO-3 is strong, stiff, dimensionally stable, and impact resistant. It is widely used for electrical insulating applications. Custom cuts and cut-to-size pieces. Have machined into fabricated parts. Stocked materials typically ship in 2-5 business days. Can’t find what you need? Get a quote.