The influences of the types of chemical blowing agent (CBA) namely endothermic, exothermic and their mixture, on the properties of the foamed poly(vinyl chloride) (PVC) and rice hull wood plastic composites (WPC) were investigated in the current research. Specifically, azodicarbonamide and sodium bicarbonate were selected to represent the exothermic the endothermic CBA respectively. Particles of sodium bicarbonate and azodicarbonamide were modified with 25 wt% citric acid and 20 wt% ZnO respectively, and they were used at 0 to 3.0 wt%. Maximum reduction of density by 45% was achieved when the exothermic CBA was applied at 2.0% by weight. Overall, the flexural properties decreased as the level of the CBA was increased from 0-2.0 wt%, but there was an upturn when the CBA reached 3.0 wt%. The mixture of exo/endothermic CBA illustrated the mechanical properties averaged between their parents.