Water absorption and structure of polyurethane foam being reinforced with sawdust was conducted by comparing the structure of the foam, which were the cell wall thickness and the cell size, against the properties of the foam which was the water absorbing and retention of the foam. The reason for reinforcing the foam with the filler is because polyurethane is not a water absorbing material and by reinforcing it with filler, that is water absorbent, it will help the polyurethane to be more water absorbent. Besides, this research will also determine the changes on the mechanical properties of the polyurethane foam. The combination of Polyol and Methylene Diphenyl Isocyanate (MDI) produced the Polyurethane Foam. The filler, sawdust, was then reinforced into the mixture and left to be hardened. Once hardened, the foam underwent multiple tests such as water absorption test and water retention test. This is to determine if the property change is a positive change or a negative change. It was found that, with the increase in cell size and cell wall thickness, there was an increase in water retention of the foam. As for the cell size and wall thickness of the foam, there was a decrease in water absorption, up till a certain amount of added filler content, then the water absorption increased.