Urethane Stoichiometry is the chemical relationship of the amount of reactive elastomer polymer to the amount of curing agent used.

Selection of proper stoichiometry is our responsibility, it plays an all-important part in compression set resistance, cut and tear resistance and flex fatigue resistance. When higher stoichiometry is used, flex fatigue resistance will be higher; however, the part will build up heat faster due to hysteresis. When lower stoichiometry is used, the finished material will have reduced compression set and will heat up slower due to hysteresis. The drawback to lower stoichiometry is that the material will be less resistant to flex fatigue and cuts or tears.

It’s important to try to establish whether heat build-up or flex fatigue resistance is the more important property needed for best application performance. Stoichiometry can be used to our advantage for problem-solving specific applications.

stoichiometry-graph