Specific heat measurements have been used to study the electronic excitation spectrum of the Cu regions ofinsituprepared Cu‐Nb and Cu–Nb3Sn composites having filament dimensions comparable to the superconducting coherence distance. At very low temperatures the major contribution toCpcomes from the electrons in the Cu regions so the excitation spectrum in Cu is easily accessible by this technique. Measurements show that the specific heat is far smaller than that expected if the Cu were normal, indicating that there is a well developed superconducting order parameter of about the size predicted from the de Gennes boundary conditions, i.e., about 0.3 meV. With the application of only a few millitesla, this gap is reduced by at least a factor of 10.