  We present PolySing#, a calculus that models process interaction based on
copyless message passing, in the style of Singularity OS. We equip the calculus
with a type system that accommodates polymorphic endpoint types, which are a
variant of polymorphic session types, and we show that well-typed processes are
free from faults, leaks, and communication errors. The type system is
essentially linear, although linearity alone may leave room for scenarios where
well-typed processes leak memory. We identify a condition on endpoint types
that prevents these leaks from occurring.
