  Outflow of granular materials from silos is a remarkably complex physical
phenomenon that has been extensively studied with simple objects like
monodisperse hard disks in two dimensions (2D) and hard spheres in 2D and 3D.
For those materials, empirical equations were found that describe the discharge
characteristics. Softness adds qualitatively new features to the dynamics and
to the character of the flow. We report a study of the outflow of soft,
practically frictionless hydrogel spheres from a quasi-2D bin. Prominent
features are intermittent clogs, peculiar flow fields in the container and a
pronounced dependence of the flow rate and clogging statistics on the container
fill height. The latter is a consequence of the ineffectiveness of Janssen's
law: the pressure at the bottom of a bin containing hydrogel spheres grows
linearly with the fill height.
