Mechanism of action hydroxypropyl cellulose is a derivative of cellulose that is soluble in both water and organic solvents. it is particularly good at trapping water and producing a film that serves as a barrier to water loss. hydroxypropyl cellulose possesses good surface activity but does not gel as it forms open helical coils. in general hydroxypropyl cellulose is a water-soluble thickener, emulsifier and film-former often used in tablet coating.