Abstract: A thin flexible humidity sensor and indicator of sandwich construction sealably mounted in an opening in the wall of a container provides a visual indication of the humidity within the container. The humidity sensor and indicator has an intermediate layer of flexible humidity sensitive material chemically treated to change color corresponding to exposure to predetermined levels of humidity, a thin flexible layer of transparent water vapor barrier material on one side, and a thin flexible layer of water vapor permeable material on its opposite side which are sealed together and sealably secured over the opening in the container wall. The water vapor permeable layer is disposed on the interior of the container and provides communication between the container interior and the humidity sensitive layer and the transparent water vapor barrier layer and the humidity sensitive layer are visible from the exterior of the container to provide a visual indication of the value of the humidity within the container.