The rubber industry is nowadays facing the general increase of raw materials as the customers are confronted with rising prices for energy. Therefore there is a need for higher durability of elastomer applications. Short fiber reinforced elastomers can contribute to the improvement of dynamic and wear properties. To determine structure-property relationships in short fiber reinforced elastomer compounds it is of crucial interest to know the contributions of fiber aspect ratio, volume content, orientation and fiber-elastomer interaction. Therefore the influence of different processing conditions and fiber contents on the resulting morphology and macroscopic properties was investigated in this article by the help of fluorescence and confocal laser microscopy using a transparent ethylene-propylene-diene rubber (EPDM) matrix. It was found that the processing induced fiber breakage was the key factor in determining the composite morphology and subsequent physical properties. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1682-1690, 2013