  A soap film, or a flexible membrane without bending and torsional stiffness,
that is confined in a cylinder is shown to be susceptible to a
surface-tension-driven instability when it is stretched or twisted. This leads
to its breakdown and places an upper limit on the aspect ratio of such
structures. A simple analysis confirms the values for the critical aspect ratio
of the stretched film found in both simulations and experiments on soap films,
and this threshold decreases with increasing twist of the film.
