Cure Terms Glossary

Isocyanate Index

A term widely used in polyurethane foam technology, the isocyanate index is the excess of isocyanate over the theoretical amount for (1:1) reaction with all active H expressed in percentage terms (i.e. 1:1 = 100). Thus,

Isocyanate index = 100 x (Actual amount of NCO used) / (Theoretical amount of NCO required)

For water-blown foams, one molecule of water can consume two equivalents of isocyanate (one to generate CO2 and one to react with the amine produced). Thus the NCO index is

The alternative convention (e.g. for PU elastomers) is the stoichiometry.