In order to minimize the effects of compositional variation in multiphase, multicomponent polymer mixtures equivalent to those found in commingled waste streams, such as those obtained from reclamation/recycling operations of post-consumer containers, several plastic composites containing varying amounts of glass fiber and different compatibilizers/coupling agents are studied. The glass-fiber reinforced composites, based on characteristic compositions simulating post-consumer “curbside tailings”, have been designed and molded into thin-section parts. Structural, and flow analyses were performed with commercial software on different types of plastic parts. Most of the data used in the simulation were experimentally generated on the compatibilized HDPE based polymer blends containing 20% short glass fibers. Issues concerned with injection molding and product performance are discussed.