Properties are identified which pass through a maximum when the filler loading in a polymer is increased; all are failure properties. Under standard test conditions of strain rate and temperature, the order of the failure property maxima with increasing filler loadings is identical in different polymers. The optimum level for maximum tear strength is higher than the optimum level for tensile strength. In general, the optimum level is even higher for abrasion resistance. The order in which these maxima develop is different when the degree of crosslinking is increased. The optimum level depends on characteristics of the polymer, e.g., the glass transition temperature. It can be shown that an increase in the pore volume of silica fillers, or an increase in the length of the crystalline segment in thermoplastic elastomers, leads to similar property trends as increased filler levels. Thus, the property trend which was established for increasing filler levels provides a scheme against which polymer or compound modifications can be assessed. The implications of the observed property trends on several generalizations in the literature are assessed.