Hydroxypropyl methylcellulose (HPMC), is a semisynthetic, inert, viscoelastic polymer that is used in many different applications. Ranging from medical eyedrops to gelatin replacements for food to thickeners in the construction industry. 

When dissolved in water it forms colloids, which in turn act as a thickener in applications such as cement renders, gypsum products, tile adhesives, and coatings. 

It has very similar properties to Hydroxyethyl methylcellulose (HEMC)