  Although soap films are prone to evaporate due to their large surface to
volume ratio, the effect of evaporation on macroscopic film features has often
been disregarded in the literature. In this work, we investigate experimentally
the influence of environmental humidity on soap film stability. An original
experiment allows to measure both the maximum length of a film pulled at
constant velocity and its thinning dynamics in a controlled atmosphere for
various values of the relative humidity $\RH$. At first order, the
environmental humidity seems to have almost no impact on most of the film
thinning dynamics. However, we find that the film length at rupture increases
continuously with $\RH$. To rationalize our observations, we propose that the
film bursting occurs when the thinning due to evaporation becomes comparable to
the thinning due to liquid drainage. This rupture criterion turns out to be in
reasonable agreement with an estimation of the evaporation rate in our
experiment.
