Thermophore Moisture-Plus Cover fits over the Thermophore Pack like the flannel cover does, but is designed so moisture can be added in the form of a damp cloth. The heating unit is protected by a rubberized cover and the damp cloth is placed in a separate sleeve. Thermophore Moisture-Plus Cover will enable your Thermophore Pack to operate at its peak efficiency, independent of atmospheric moisture conditions. New, non-shrinkable "flannel" cover, made of cotton/fleece. Use medium setting so that cover does not become excessively dry.