The shear test data for the PP specimens were statistically analyzed to estimate the effect of aluminum surface roughness and glass fiber content. The analysis of variance reported what is evident from the shear strength results in Table 1: the reinforcement fiber content has a strong effect on the interface bonding strength whereas the influence of surface roughness is only secondary at this level. The higher the fiber content the stronger the bonding interface. This result was further confirmed by preliminary experimental tests conducted with non-reinforced PP: after removal of the test specimens from the mold, while the parts were cooling to room temperature, the overmolded plastic plates significantly shrank, delaminating from aluminum sheet.