Abstract: An irreversible humidity indicator having a delayed response time includes a porous plastic carrier having upper and lower opposing surfaces, the upper surface including a depressed region for containing a deliquescent agent coated with a water soluble dye. A sheet of blotter paper overlies the upper surface of the porous plastic carrier and contacts the dye-coated deliquescent agent for absorbing the water soluble dye, and thereby providing an irreversible indication, when the humidity level directly surrounding the deliquescent agent is sufficiently high to dissolve the deliquescent agent. The plastic porous carrier is packaged to isolate the upper surface thereof from direct exposure to the environment to be monitored, and the density and thickness of the plastic porous carrier are selected to delay the passage of moisture-laden air from the lower surface to the depressed region thereof for a predetermined time.