The Stupe 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. The Stupe 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.