Hydroxyethylmethacrylate or HEMA is the monomer that is used to make the polymer polyhydroxyethylmethacrylate. The polymer is hydrophobic; however, when the polymer is subjected to water it will swell due to the molecule's hydrophilic pendant group. Depending on the physical and chemical structure of the polymer, it is capable of absorbing from 10 to 600% water relative to the dry weight. Because of this property, it was one of the first materials to be successfully used in the manufacture of flexible contact lenses