  We study the behavior of dust in galaxies at cosmic dawn, z=6-8, by coupling
the FirstLight simulations with the radiative transfer code POLARIS. The
starburst nature of these galaxies and their complex distribution of dust lead
to a large diversity of attenuation curves. These follow the Calzetti model
only for relatively massive galaxies, Mstars=10^9Msun. Galaxies with lower
masses have steeper curves, consistent with the model for the Small Magellanic
Cloud (SMC). The ultraviolet and optical slopes of the attenuation curves are
closer to the modified Calzetti model, with a slight preference for the
power-law model for galaxies with the highest values of attenuation. We have
also examined the relation between the slope in the far-ultraviolet, beta_UV ,
and the infrared excess, IRX. At z=6, it follows the Calzetti model with a
shift to slightly lower beta_UV values due to lower metallicities at lower
attenuation. The same relation at z=8 shows a shift to higher IRX values due to
a stronger CMB radiation at high-z.
