Isophthalic resins (abbreviated as “Iso resins”), are a type of unsaturated polyester resins used for making composite components with improved performance and higher quality. Isophthalic resins provide higher toughness, tensile elongation, and improved resistance to chemicals compared to Orthophthalic and DCPD resins. Heat resistance in some cases may be a bit lower.

The basic chemistry of the resin backbone consists of a combination of maleic anhydride and isophthalic anhydride, and different types of glycols (e.g. monopropylene glycol, monoethylene glycol, dipropylene glycol, neopentyl glycol).

In the manufacturing process at AOC, these ingredients are combined into an unsaturated polyester chain through a poly-condensation reaction, and then diluted with a reactive monomer (in most cases styrene) and other ingredients to make a finished resin. Our customers combine the resin with specific peroxides, so a chemical reaction is initiated between resin backbone and the styrene, transforming the liquid into a hard and durable material.

Iso resins are used as laminating resin in multiple processes like Filament Winding, Pultrusion, Hand lay-up, Spray-up. In addition, Iso resins and in particular Iso/ NPG resins are used as base resin for making gelcoats, because of their excellent weathering resistance. Consequently, Iso resins are used in Industrial (tanks, pipes, industrial equipment, and water transport), Marine (boatbuilding), Transportation, Building & Infrastructure (sanitary components, façade panels, and profiles).



AOC has a broad range of products based on Iso resin chemistry in its portfolio, sold under Synolite™, Palatal® and Palapreg® product brands. In order to find the best product for your application, please check out the Product Selector on this web site. You can contact an AOC Technical Service representative for helping you in the selection process (




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