Morphology of carbon black (CB)-filled rubber was studied with AFM and SEM and the classification of filler agglomerates, based on their internal Structure and filler-matrix interactions, has been proposed. It varies according to the activity of CB and the kind of rubber. It has been shown that fracture of rubber starts either inside filler agglomerates (de-cohesion) or in a filler-matrix interphase (de-adhesion) initiating wear of the material. Microscopic observations correlate well with TGA and EPR data of wear debris collected during friction of rubber. The increase of thermal stability of CB,and the appearance of additional spin signals, respectively, for elongated samples or debris, are proposed to be associated with de-cohesion or de-adhesion of the agglomerates. New approach to the fracture of rubber called "fatal agglomerate concept" is presented. (C) 2008 Wiley Periodicals, Inc.