Mix a polyol and an isocyanate and they will react on their own — but slowly, and without much control. Catalysts are what turn that raw reaction into a manufacturable process, deciding how fast the foam rises, when it gels, and how its cells form. Two families do most of the work: amine catalysts and tin catalysts.
Two reactions, not one
Polyurethane foam actually involves two reactions happening together. The gel reaction builds the polymer network (polyol + isocyanate), while the blow reaction generates the gas that expands the foam (isocyanate + water producing CO₂). A good foam needs these two in balance — and catalysts are how you balance them.
Amine catalysts
Amine catalysts primarily drive the blow reaction and help control rise, stability and surface quality. By selecting and blending amines, a formulator can speed up or slow down gas generation and fine-tune how the foam develops. They are used across flexible slabstock, rigid panels and moulded parts. See our amine catalysts.
Tin catalysts and stannous octoate
Tin catalysts — most commonly stannous octoate (tin II 2-ethylhexanoate) — push the gel reaction, accelerating urethane formation and giving processing control in flexible foam. Stannous octoate is a staple of flexible slabstock production and works hand in hand with amine catalysts.
Why most foams use both
Because the gel and blow reactions must stay in step, most foam systems use an amine catalyst and a tin catalyst together. Tip the balance toward blow and the foam may rise before it has the strength to hold; tip it toward gel and it may set before it has fully expanded. The catalyst package is, in effect, the timing system of the foam.
Beyond catalysts
Catalysts rarely work alone. Silicone surfactants stabilise the cell structure, blowing agents help expand the foam, and flame retardants and colorants finish it. Together with the right polyol and isocyanate (TDI or MDI), they make up the complete system.
Getting the package right
Catalyst selection is sensitive and application-specific. If you are developing or troubleshooting a foam, our team can advise on an amine/tin balance suited to your line and target properties.
Creston Chem supplies polyols, TDI, MDI and polyurethane additives to manufacturers across India. For grade-specific guidance, talk to our desk.