Unsaturated Polyester Resin

Unsaturated Polyester Resin is a thermosetting resin used in compression molding compounds. This page covers its classification and a documented finding on how cure temperature affects how fully the resin cures.

What is it?

Unsaturated Polyester Resin is classified under ASTM D1201 as a thermosetting polyester molding compound, with defined classification, requirements, and testing for compression molding compositions.

Why should I use it?

1. A single specification classifies its compression molding compositions — see “What is it?” above.
2. How fully it cures is directly tied to processing temperature — see Limitations.

How it’s used

In Plastics & Polymers, Unsaturated Polyester Resin is used in compression molding compounds classified under ASTM D1201.

Limitations — when it isn’t the right choice

• Curing at too low a temperature leaves the resin under-cured. A 2024 peer-reviewed study modeling cure behavior of an unsaturated polyester resin system found that as processing temperature increased from 10°C to 170°C, the cure rate declined while the heat of reaction increased. The maximum degree of cure reached 71.25% at an 85°C heating temperature, but at 5°C, the maximum degree of cure stayed below 12%, because there wasn’t enough heat to activate the catalyst. This was documented for one specific resin system under tested processing conditions; it should not be assumed to apply identically to every commercial unsaturated polyester formulation.