  We point out a new simple way to couple the Gaussian Free Field (GFF) with
free boundary conditions in a two-dimensional domain with the GFF with zero
boundary conditions in the same domain: Starting from the latter, one just has
to sample at random all the signs of the height gaps on its boundary-touching
zero-level lines (these signs are alternating for the zero-boundary GFF) in
order to obtain a free boundary GFF. Constructions and couplings of the free
boundary GFF and its level lines via soups of reflected Brownian loops and
their clusters are also discussed. Such considerations show for instance that
in a domain with an axis of symmetry, if one looks at the overlay of a single
usual Conformal Loop Ensemble CLE(3) with its own symmetric image, one obtains
the CLE(4)-type collection of level lines of a GFF with mixed zero/free
boundary conditions in the half-domain.
