The 22 lm mAC was found to be most efficient in reducing the density of the foamed composites when it was applied at 2.0 wt.%. There was a dramatic density reduction by 46% as compared with the unfoamed one. With identical mAC content, the larger mAC particles tend to lower the foam density more significantly than the smaller ones. Minimum PVC/rice hull foam density was observed at 2.0 wt.%. mAC content. The flexural modulus decreased as the level of the mAC was increased from 0 to 2.0 wt.%.