Injection stretch blow molding process for preparing polyolefin containers, comprising the following steps: 1) preparing a preform by injection molding a polyolefin composition comprising a polymer (A) selected from ethylene polymers, propylene polymers and mixtures thereof, and a heat absorber (B); 2) supplying heat to reheat the preform prepared in step 1) and stretch blow molding said preform; wherein the heat absorber (B) is selected from phosphates, condensed phosphates, phosphites, and mixed hydroxide/phosphate oxanion compounds of Copper (Cu), Calcium (Ca), Tin (Sn) and/or Iron (Fe).