Cornstarch is an excellent substitute for potato starch. The ingredients are interchangeable in equal amounts. Both starches are popular thickening agents, and the primary difference between them is that cornstarch produces a more opaque result. However, About.com explains that cornstarch is not a suitable baking substitute for potato flour, which has a forceful potato taste.
Tapioca starch is also an excellent substitute for both cornstarch and potato starch. It is gluten-free and has a mild flavor. In baked goods, however, tapioca starch produces a chewier, tougher texture than cornstarch and potato starch. Many cooks mix tapioca starch with cornstarch or potato starch to avoid overly tough results.
Another excellent substitute for cornstarch and potato starch is konjac flour, which has no calories or gluten. FitDay states that konjac flour has no discernible taste and is useful for diabetics because it does not contain sugar. This vegan ingredient is also a popular substitute for gelatin.
White and brown rice starches and flours are also effective substitutes for cornstarch, potato starch and wheat flours. White rice starch has a faintly gummy texture when wet and adds noticeable rice flavor to many dishes. Brown rice flour has a milder flavor. Rice starches and flours are popular gluten-free alternatives to traditional wheat flours, particularly in Asian cuisines.