When the first one (Hc1) is reached, magnetic field lines begin penetrating the material though it still retains superconductivity—that is, until it reaches its second threshold (Hc2). This second critical field boundary is usually much higher than Hc found in Type I superconductors, which is why Type II superconductors are preferable in many engineering applications.

For instance, Type II superconductors like niobium titanium (NbTi) are used to create high-field superconducting magnets for various types of fusion reactors. The ITER tokamak based in Saint-Paul-lez-Durance, France, uses NbTi in its poloidal field coils, which are essential in plasma confinement. Meanwhile, the Wendelstein 7-X stellarator in Greifswald, Germany, uses NbTi for its magnets.