This study has created a new way of microcellullar processing PET thin sheet foam using a conventional hydraulic press by compression molding and by setting the temperature of press plates differently. Comparing this study with our previous work, the emphasis is on the difference of plate temperature. The nonisothermal condition is used to control the foaming agent decomposition to lead to more uniform cell size microcellular foam. A variety of cell sizes, cell densities, and relative densities are obtained as a consequence of the different foaming temperature, time, pressure, and foaming agent content via isothermal and nonisothermal conditions. The effect of isothermal and nonisothermal foaming on the cell size, cells density, and relative density has been discussed. The electrical properties of the microcellular poly(ethylene terephthalate) (PET) samples prepared in nonisothermal foaming have been investigated. The experimental results show that the microcellular PET foam has lower dielectric constant and dielectric loss and higher electric resistivity than unfoamed PET. (C) 2004 Wiley Periodicals, Inc.