The water vapor permeability (WVP) of the HPMC films and HPMC-based composite films was determined using a gravimetric modified cup method according to ASTM E96. Films selected without defects and pinholes were cut and sealed to the cup base previously filled with 7 ml distilled water. The cup was then placed into a cabinet at 27 ± 3 C and 50% (RH).