  The purpose of this talk is to sketch some recent progress which has been
made in calculating non-perturbatively the reflection factors for the
sinh-Gordon model restricted to a half-line by integrable boundary conditions.
The essential idea is to calculate the energy spectrum of boundary breathers in
two independent ways; firstly by using the boundary bootstrap and secondly by
quantizing the classical solutions corresponding to boundary breathers.
Comparing these two calculations provides a way to determine the dependence of
the reflection factors on the parameters introduced into the Lagrangian by the
boundary conditions. The basic idea is illustrated using a massive free scalar
field with a linear boundary condition confining it to a half-line.
