There are a few ingredients that can be substituted for two tablespoons of quick-cooking tapioca powder, including flour, cornstarch and pearl tapioca. However, the proportions of these different ingredients will vary.
For two tablespoons of tapioca, the substitute proportion for flour is two tablespoons. When substituting cornstarch for tapioca, the proportion is one tablespoon of cornstarch per two tapioca tablespoons. Likewise, four tablespoons of soaked pearl tapioca is a substitute for two tablespoons of the quick-cooking variety.
Tapioca is a thickener used in pies, puddings, soups and gravies. Tapioca is the starch extracted from the roots of the cassava or manioc plant.