This report describes the details of the single fiber fragmentation test as conducted at the materials research department (AFM) at Risø. The equipment and specimen manufacture is described in detail. Furthermore, examples of results interpretation are given. For the experiments in this report, specimens with one E-glass fiber placed inside an epoxy or polyester matrix were used. Elongating the specimens with a mini tensile tester, which was placed under a microscope, leads to fiber fragmentations. Different bonding strengths between fiber and matrix result in differences in the critical fracture length for the fiber and fracture characteristics.