A blocked isocyanate can be added to materials that would normally react with the isocyanate such as polyols. They do not react at normal ambient room temperature. A formulation containing a blocked isocyanate is a single component material (and thus usually considered more convenient) but reacts like a two-component product but will not react until heated to the temperature required for activation which varies depending on the blocking agent. The shelf lives when stored at ambient temperature have been reported as good. On heating up to the activation temperature, cure can be as short as 20 minutes depending on the blocking agent and other formulation parameters.
Blocked isocyanates are particularly useful in products with a dual cure mechanisms. As an example,  Ultraviolet light initiates the polymerization of an acrylate based polymer that contains hydroxy groups on the polymer backbone. The system would also contain an isocyanate blocked with a malonate. This is now a  one-component system. When heat is applied, the polymerization is initiated. Higher temperatures then unblock the isocyanate, allowing the cure and crosslinking of the urethane.