  The lepton propagator PROPOSAL is a Monte-Carlo Simulation library written in
C++, propagating high energy muons and other charged particles through large
distances of media. In this article, a restructuring of the code is described,
which yields a performance improvement of up to $30\,\%$. For an improved
accuracy of the propagation processes, more exact calculations of the leptonic
and hadronic decay process and more precise parametrizations for the
interaction cross sections are now available. The new modular structure allows
a more flexible and custom usage, which is further facilitated with a python
interface.
