Unsaturated polyester resins are formed by the reaction of dibasic organic acids and polyhydric alcohols. These are the most widely used and economical family of resins. Polyester resins have adequate water and chemical resistance, good wetting of glass fibers, enough mechanical properties and low cost. Orthophthalic and isophthalic polyesters are two principle types of unsaturated polyester resins. Isophthalic in comparison with orthophtalic offers substantially higher tensile and flexural strength, better flexibility and chemical resistance.
Polyester resins are used in production of pipes, tanks, boats, artificial stone, FRP panels, building and decorative objects.