Post-curing polyurethane: why, how long and at what temperature

Polyurethane cures at room temperature — and yet we almost always recommend post-curing. The reason: room temperature is too low for the material to develop all of its properties. Post-curing — placing the cured PU part in an oven at raised temperature for a while — drives the polymerisation through to completion.

What post-curing gives you

The molecular bonds in the polyurethane are strengthened. The material becomes stronger, more impact-resistant and better able to handle temperature swings. That matters most for applications with high mechanical loads or changing conditions: technical parts, prototypes that will be tested, and anything destined for outdoor use.

A second, less-discussed benefit: unreacted material can no longer migrate out of the part. That saves you bleeding and discolouration over time.

In or out of the mould

Post-curing usually happens after demoulding, but it can be done in the mould. If you do it outside the mould, keep the temperature below the glass transition temperature of the product. Above that point the part deforms under its own weight — exactly what you were trying to avoid.

Time and temperature

The duration varies, but expect several hours. The exact time and temperature depend on the type of polyurethane and the properties you want. Follow the data sheet for your specific system; a general rule of thumb does more harm than good here, because the glass transition temperature differs sharply between systems.

Post-curing too hot is more damaging than not post-curing at all. When in doubt, go lower and run it longer.

Which oven

Use a separate oven that is not used for food. This prevents cross-contamination and is a basic condition for working safely with these materials.

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Not sure about the right post-cure for your application? Ask our technical team — we have the data sheets for all our polyurethane systems to hand.