A ferrosmectic is a swollen lamellar phase in which solid magnetic particles have been incorporated. We measure the elastic constants of these phases, and compare them to conventional lyotropic smectic phases. It is shown that both the bending and the compression elastic constants are largely enhanced by the presence of particles and that their evolution can not be accounted for by the usual models for lamellar phases. A phenomenological model of enhanced repulsive potential between membranes based on steric considerations is developed and confronted to experimental results.