  Drops placed on a surface with a temperature above the Leidenfrost point
float atop an evaporative vapor layer. In this fluid dynamics video, it is
shown that for roughened surfaces the Leidenfrost point depends on the drop
size, which runs contrary to previous claims of size independence. The
thickness of the vapor layer is known to increase with drop radius, suggesting
that the surface roughness will not be able to penetrate the vapor layer for
drops above a critical size. This size dependence was experimentally verified:
at a given roughness and temperature, drops beneath a critical size exhibited
transition boiling while drops above the critical size were in the Leidenfrost
regime. These Leidenfrost drops were unstable; upon evaporation down to the
critical size the vapor film suddenly collapsed.
