  Topological insulators are materials where current does not flow through the
bulk, but along the boundaries, only. They are of particular practical
importance, since it is considerably more difficult, by ``conventional'' means,
to affect their transport properties, than for the case of conventional
materials. They are, thus, particularly robust to perturbations. One way to
accomplish such changes is by engineering defects. The defects that have been
the most studied are domain walls; however flux compactifications can, also,
work. We recall the domain wall construction and compare it to the construction
from flux compactification.
  A particular way of engineering the presence of such defects is by
introducing anisotropic couplings for the gauge fields. In this case a new
phase appears, where matter is confined along layers and local degrees of
freedom cannot propagate through the bulk. It is, also, possible to take into
account the ``backreaction'' of the dynamics of the gauge fields on the defects
and find that a new phase, the layered phase, where, while transport of local
degrees of freedom is confined to surfaces, the topological properties can
propagate through the bulk, constituting an example of anomaly flow.
  The anisotropy itself can be understood as emerging from a particular
Maxwell--dilaton coupling.
