The strong interaction between rubber and filler leads to the formation of an interphase region at the boundary. Its properties differ from the properties of the remaining matrix, and it has a considerable influence on the properties of the elastomeric composite. The dependence of the volume fraction of interphase polymer layer φδ on the volume fraction of filler φf for particles of different shape and structure was calculated. The values of φδ for the individual particles and linear aggregates are higher than for aggregates of ellipsoidal structure. All dependences pass through a maximum at different φf: for individual particles and linear aggregates roughly at φf = 0.1, for aggregates of ellipsoidal structure at φf = 0.3. The results were compared with data on the adsorption of dibutyl phthalate by different grades of carbon black (CB) having an identical specific surface (N326, N330, N351, N358). The more CB aggregates accessible to elastomer molecules there are, the higher is φδ. Thus, CBs of chain structure have, at all φf, higher φδ values than CBs with aggregates of ellipsoidal structure. The obtained results open up the possibility of predicting the optimum content of ingredients in the elastomeric composites.