The paper considers a diffusion equation in a thin domain of thickness ε in
$\mathbb{R}^{n}$
whose diffusivity varies periodically with a period cell of size εp (p>0) in the cross section. The domain is highly heterogeneous so that the diffusivity is of the scale εα (α>0) in a part of the period cell and is of order 1 in the rest. The asymptotic behaviour of the solution when ε→0 is studied for all the values of p and α. In some cases, the limiting equation is in
$\mathbb{R}^{n-1}$
as in the previous works on diffusion in thin domains but in some others, an equation in
$\mathbb{R}^{n}$
is obtained.