In Ginzburg-Landau theory, a strong magnetic field is responsible for the breakdown of superconductivity. This work is concerned with the identification of the region where superconductivity persists, in a thin shell superconductor modeled by a compact surface M ⊂ R 3 , as the intensity h of the external magnetic field is raised above Hc1. Using a mean field reduction approach devised by Sandier and Serfaty as the Ginzburg-Landau parameter κ goes to infinity, we are led to studying a two-sided obstacle problem. We show that superconductivity survives in a neighborhood of size (Hc1/h) 1/3 of the zero locus of the normal component H of the field. We also describe intermediate regimes, focusing first on a symmetric model problem. In the general case, we prove that a striking phenomenon we call freezing of the boundary takes place: one component of the superconductivity region is insensitive to small changes in the field.