I'm guessing it essentially increases the elastic constants of the material; that is, increases the "spring constants" of the bonds between atoms. As a result,

I'm guessing it essentially increases the elastic constants of the material; that is, increases the "spring constants" of the bonds between atoms. As a result, the resonant frequency of acoustic vibrations rises. When these acoustic vibrations are quantized into phonons, the minimum energy of each phonon therefore rises, since it is proportional to this resonant frequency. Since conventional cooper pairs are pairs of electrons bound by a phonon, this increases the binding energy of the pair, and makes it more resilient to being broken up by the thermal energy.