The addition of polymers is an alternative often used to modify the structure and properties of materials seeking new applications and improvements thereof. The blowing agents are chemical compounds normally incorporated in the mixture and decompose under the conditions of melt processing . The microstructure obtained in structural foams formed of injection molded thermoplastic polymer and blowing agent is added with a very complex process and depends on the conditions of processamento.As mechanical properties are influenced by the size and distribution of bubbles formed in the material. In this work were injected samples of HDPE compounds mixed with controlled amounts of between 0.5 % to 4 % of endothermic blowing agent in the form of master LDPE as vehicle and mineral filler varying parameters such as speed and injection temperature . It was determined by calcining the mineral filler content of blowing agent present in , since this acts as nucleating agent . The influence of the amount of blowing agent on microcellular structure and mechanical property . The thermal decomposition temperature of the expander was determined by DSC . We characterized the mechanical behavior by tensile and impact and morphology in SEM. The results indicate that the amount of expander changes the microstructure formed and the greater the quantity more gas was generated , then higher diffusivity in the polymer melt .