  We compare observed far infra-red/sub-millimetre (FIR/sub-mm) galaxy spectral
energy distributions (SEDs) of massive galaxies ($M_{\star}\gtrsim10^{10}$
$h^{-1}$M$_{\odot}$) derived through a stacking analysis with predictions from
a new model of galaxy formation. The FIR SEDs of the model galaxies are
calculated using a self-consistent model for the absorption and re-emission of
radiation by interstellar dust based on radiative transfer calculations and
global energy balance arguments. Galaxies are selected based on their position
on the specific star formation rate (sSFR) - stellar mass ($M_{\star}$) plane.
We identify a main sequence of star-forming galaxies in the model, i.e. a well
defined relationship between sSFR and $M_\star$, up to redshift $z\sim6$. The
scatter of this relationship evolves such that it is generally larger at higher
stellar masses and higher redshifts. There is remarkable agreement between the
predicted and observed average SEDs across a broad range of redshifts
($0.5\lesssim z\lesssim4$) for galaxies on the main sequence. However, the
agreement is less good for starburst galaxies at $z\gtrsim2$, selected here to
have elevated sSFRs$>10\times$ the main sequence value. We find that the
predicted average SEDs are robust to changing the parameters of our dust model
within physically plausible values. We also show that the dust temperature
evolution of main sequence galaxies in the model is driven by star formation on
the main sequence being more burst-dominated at higher redshifts.
