DS: the substituent of HPMC is Hydroxypropyl and Methoxy. The ratio of them affects HPMC properties. The higher the hydroxypropyl content, the better the water retention effect. The lower the methoxy content, the higher the gel temperature. The DS of HPMC is 1.2-2.0. But HEC substituent is Hydroxyethyl substituent. Its DS is 1.5-2.0.