[DNU] PVA (polyvinyl alcohol) is an example of a water soluble plastic. Essentially how it achieves this is that they replace the polymer's acetate molecules with alcohol molecules that help to attract water molecules, which in turn, causes the plastic to dissolve in water. However, the rate of solubility is determined by the amount of acetate molecules that are replaced with alcohol molecules. PVA is also insoluble in organic chemicals, such as gasoline, grease, fats, and other oils. "And now you know the rest of the story." [DNU]