  The process of forming a circumbinary planet is thought to be intimately
related to the structure of the nascent circumbinary disc. It has been shown
that the structure of a circumbinary disc depends strongly on 3-dimensional
effects and on the detailed modelling of the thermodynamics. Here, we employ
3-dimensional hydrodynamical simulations, combined with a proper treatment of
the thermal physics using the RADMC-3D radiation transport code, to examine the
location of the snow line in circumbinary discs. The models have application to
the circumbinary planets that have been discovered in recent years by the
Kepler and TESS transit surveys. We find that the snow line is located in a
narrow region of the circumbinary disc, close to the inner cavity that is
carved out by the central binary, at typical orbital distances of $\sim 1.5-2$
AU for the system parameters considered. In this region, previous work has
shown that both grain growth and pebble accretion are likely to be inefficient
because of the presence of hydrodynamical turbulence. Hence, in situ planet
formation interior to the snow line is unlikely to occur and circumbinary
planets should preferentially be icy, not rocky.
