AbstractPhysical properties of composites as a function of filler content have been described in the past through models requiring the solution of macroscopic equations of motion for an elastic continuum or, on a more empirical level, by the assumption of various compositional averaging schemes. We discuss a model drawn from our molecular mixture theory. This allows us to avoid the formal problems attending concentrated suspensions and introduces molecular filler‐medium interaction parameters. Comparisons with experimental material and empirical equations involving bulk modulus and thermal expansivity will be given. The theory opens the possibility of determining interfacial strengths from appropriate mechanical and thermal measurements and of predicting one set from another set of dat