The present invention provides a time-temperature integrating indicator having an amorphous material in operable contact with a porous matrix, wherein the amorphous material only migrates into the porous matrix at or above a predetermined temperature. Use of the invention simplifies monitoring of the cumulative temperature exposure of the product because no additional actuation step is required. The indicator is especially useful in monitoring the cumulative time-temperature exposure of a perishable product for a short period of time at an abusive temperature.