This report is the final task of course “42234 Eksperimentel plastteknologi in the 3-week period of June 2007 at DTU, IPL. The report deals with effects of short glass fibers on the replication quality of thin ribbed structures. The aims of the project work were proposed as: - Investigate the effects of the glass fibers on the replication of polymeric ribs. - Investigate fibers orientations based on the injection parameters - Geometrical size effect on the amount of glass fibers in the post moulded plastic parts. Several tests were carried and analyzed in order to investigate the three project aims. Mainly test were made on injections moulded parts produced in the first week of the course. From the analysis of the tests conclusions were drawn: • Fiber reinforced polymers are not well suited for micro structures, due to negative effects of fibers on replication quality. • PEI as a polymer is much better suited to micro moulding with high tolerances than PS. • Injection parameters for PEI need to be tailored to fit the specific demands of the micro moulded parts. A compromise between surface quality, and edge sharpness needs to be considered. • The addition of glass fibers to the injection moulding melt will cause the material to get stiffer (higher modulus of elasticity). The added stiffness affects the materials ability to eject from the mould without creating permanent defects on the specimen. • The distribution of fibers will vary depending on the geometry of the moulded parts.