was raised. Maximum cell density was observed at 2.0 wt.% as shown in Fig. 4 and verified by the associated microstructure shown in Fig. 5d. Fig. 4 reveales that at identical mAC content, the large mAC particles at 22 lm led to greater cell density than the smaller particles, especially at 2.0 wt.% when the cell density was maximized at 30.08 106 cells/cm3. The lowest cell density was found when 0.5 wt.% of mAC 5 was applied. At small contents of fine mAC particles such as at 0.5 and 1.0 wt.%, the numbers of foam cells were apparently lower than those at high content of mAC. This is confirmed by the SEM micrographs shown in Fig. 5.