U.S. patent application 20170340008 (applicant R.J. Reynolds Tobacco Co., Winston-Salem, N.C.):
"A smoking article is disclosed herein. The smoking article includes a shell defining an interior space, a consumable substance within the interior space, a heat source effective to increase the temperature of at least a portion of the shell, and a label attached to at least a portion of the shell. The label includes a base film, a cover film, and a temperature dependent material disposed between the base film and the cover film. The temperature dependent material is configured to transition between a first appearance and a second appearance responsive to the increase of the temperature of at least a portion of the shell. ... In some embodiments, the temperature dependent material may be a reversible thermochromatic ink or a reversible phase change material that may transition from a colored, opaque cool state to a substantially transparent warm state to effect the change in appearance. "