Fully burnt rice hull (rice hull ash) was tried as a low cost filler in place of precipitated
silica in NBR/PVC based microcellular soles. The mechanical properties of the soles
containing silica and ash are found to be comparable. The expansion is marginally
higher in the presence of ash, which permits to reduce the amount of blowing agent. Cell
structure of microcellular sheets remains unchanged when silica is replaced by ash.