Bimodal high density polyethylene pipe grades which were synthesized by polymerization of ethylene using Ziegler-Natta catalysts in cascade reactors , are normally characterized by their molecular weight, molecular weight distribution, vico-elastic properties and branching indexes. This approach of characterization is not capable of complete rationalization of remarkable hydrostatic pressure and charpy impact resistances observed in PE 100 pipes .Multiple endothermic peaks obtained from SSA analysis which attributed to heterogeneity of ethylene sequence length, lamellar thickness and also the non-uniformity of SCB, proposed a blend structure of high density polyethylenes in PE 100 grade. This blend is a mixture of compatible co-crystallized phases with different crystalinity, forming a physical semi hard and soft segment network responsible for improved impact properties in PE 100 pipe grade. Nevertheless many researchers have investigated the characteristics of high impact polypropylene grades as in-reactor blends, HDPE bimodal tough grades have been neglected in this point of view. In this work by comparing GPC, RMS, FTIR AND SSA results of industrial 1-butene OFF and ON PE 100 grades to a reference grade produced in the same process with different catalyst, we showed that it is the content and structure of semi hard and soft segments that determines the improved properties of these grades rather than other micro-structures. For producing a tailor-made HDPE pipe reactor alloy, an special molecular and crystal-amorphous architecture is needed which is dictated by both catalyst nature and process. We also showed that controlling of 1-butene content in the first reactor in cascade technology is the main processing parameter affecting the the semi hard and soft segment network in the final resin leading to proper hydrostatic pressure and Charpy impact resistances of produced pipes. This new approach can also be utilized for describing the tough behavior of bimodal HDPE film grades used in the multi layered packaging films produced in cascade processes.