Packaging material and products comprising indicia-former which changes from a first visual condition to a second visual condition and indicates a characteristic of the package contents

Packaging materials, in particular, film and products that are marked with an energy sensitive indicia-former. The film has at least one heat sensitive indicia-former on at least part of the film. The film comprises a thin film substrate which is substantially transparent to radiant energy. Associated with at least part of the film substrate is an absorbent material which is sufficiently opaque to radiant energy to absorb said radiant energy and convert the radiant energy into heat energy. The indicia-former undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy from the absorbent material. The film is used preferably as a shrink wrap of the open top of drink containers and to identify the contents of the container.