The water absorption is a measure of a material's stability in high moisture environment condition. Polymeric materials absorb varying amounts of water, and the presence of the absorbed water may affect the material in different ways. For example, the eletrical properties can be reduced with moisture absorption. Mechanical properties such as yield stress, modulus of elasticity and hardness tend to be reduced with higher moisture absorption while impact resistance and elongation will increase. Physically, high moisture absorption can also cause significant changes in dimension and weight. For a certain dental application, the moisture absorption can lead to staining and instability of biocompatibility. The value for water absorption is obtained by immersion for 24 hours or longer in water at around room temperature, and then taking the ratio of the increase in weight.