Components made from fiber-reinforced thermoplastics show good weight specific mechanical properties and can be manufactured in a cost efficient way using injection molding. By combining this material group with foam injection molding (FIM) the lightweight potential can be further improved. The result is a single material system with a sandwich-like structure: fiber-reinforced foamed core and compact skin layers. Different FIM processes are available on the market. Chemical blowing agents (CBA) in combination with a standard injection molding set-up and the use of physical blowing agents (PBA) with the MuCell® technology are common. CBAs are admixed to the polymer and split of gases above certain process temperatures. PBAs are introduced directly into the melt. Using these processes glass-fiber-reinforced polyamide 6 (PA6) foams were manufactured with a constant weight per unit area and varying density reductions. Precision mold opening (breathing mold technology) was selected for the foaming process. This technology allows higher density reductions and a definite adjustment. The injection compression mold is opened after injection, enlarging the cavity to its final volume and causing a pressure drop which initiates the foaming process. The average fiber length has a significant influence on the mechanical properties. Especially the energy absorption capacity (impact strength) of fiber-reinforced foam components correlate with the fiber length. This means that for processing the objective must be to preserve the fibers during the plastification and injection. Investigations into different semi-finished granulates have been carried out using different screw designs: standard three-section screw design and fiber-preserving screw geometry at the mixing zone. The focus of this study is FIM of glass-fiber-reinforced PA6 using CBAs and PBAs. Experiments show the influence of density reduction, material and processing on the mechanical properties and the foam structure.