  It has been a common assumption of interior models that the outer planets of
our solar system are convective, and that the internal temperature
distributions are therefore adiabatic. This assumption is also often applied to
exoplanets. However, if a large portion of the thermal flux can be transferred
by conduction, or if convection is inhibited, the thermal profile could be
substantially different and would therefore affect the inferred planetary
composition. Here we investigate how the assumption of non-adiabatic
temperature profiles in Uranus and Neptune affects their internal structures
and compositions. We use a set of plausible temperature profiles together with
density profiles that match the measured gravitational fields to derive the
planets' compositions. We find that the inferred compositions of both Uranus
and Neptune are quite sensitive to the assumed thermal profile in the outer
layers, but relatively insensitive to the thermal profile in the central, high
pressure region. The overall value of the heavy element mass fraction, $Z$, for
these planets is between 0.8 and 0.9. Finally, we suggest that large parts of
Uranus' interior might be conductive, a conclusion that is consistent with
Uranus dynamo models and a hot central inner region.
