Hypromellose Phthalate (Hydroxypropyl Methylcellulose Phthalate) is a phthalic half ester of Hypromellose and the threshold pH value for rapid disintegration of HPMCP can be controlled by varying the phthalyl content.

HPMCP is a solvent based enteric coating agent used to protect drugs from gastric degradation or to protect the gastric mucosa from irritant drugs.

Two types of HPMCP are available based on the pH solubility, HP-50 and HP-55. Additionally, there is a special type viz, HP-55S which has a higher molecular weight and gives films of greater strength and gastric resistance.