en Research Paper Research Paper <div style="text-align: justify;">In this work, the poly styrene-co-acrylonitrile (SAN)beads and three blowing agents (CO₂, N₂ and n-pentane) were used to investigate the foaming process via our batch foaming system. The solubility and diffusivity of three blowing agents were determined by the MSB. The solubility of blowing agents was increased by pressure and decreased by temperature increment. It was resulted that the solubility and diffusivity data for SAN/n-pentane/CO₂system (Using co-blowing gent) were higher than other samples. According to the scanning electron microscopy (SEM) results, it was concluded that the cell and foam densities were decreased with temperature increment and increased by pressure release rate in all foamed beads. With using co blowing agents, higher pressure release rate and low temperature without adding any fillers, we could improve the foam characteristics and produced the SAN foams with smaller cell sizes and greater cell and foam densities.</div> ,SAN,MSB,foaming process,co blowing agents,cellular structure 34 41 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-2444-1&slc_lang=en&sid=1 H. Azimi h.azimi@azaruniv.ac.ir 1800319475328460014645 1800319475328460014645 Yes Chemical Engineering Department, Faculty of Engineering, Azarbaijan Shahid Madani University, Postal Code: 5375171379, Tabriz, Iran.