  Thin liquid or gas films are everywhere in nature, from foams to
submillimetric bubbles at a free surface, and their rupture leaves a collection
of small drops and bubbles. However, the mechanisms at play responsible for the
bursting of these films is still in debate. The present study thus aims at
understanding the drainage dynamics of the thin air film squeezed by gravity
between a millimetric droplet and a smooth solid or a liquid thin film. Solving
coupled lubrication equations and analyzing the dominant terms in the solid and
liquid film cases, we explain why the drainage is much faster in the liquid
film case, leading often to a shorter coalescence time, as observed in recent
experiments.
