Flowstone is perhaps the most common of cave deposits. As with the vast majority of such formations, it consists of rock (usually calcium carbonate, a major component of limestone) precipitated in thin layers, over thousands or millions of years, by water.

Flowstone is distinguished from stalactites, "draperies" and other such objects primarily by its location; instead of extending up into the air or down from a cavern's ceiling, it is deposited over existing stone. At first, it has almost exactly the shape of the underlying rock, but as more flowstone is deposited it usually takes on rounded, almost organic shapes that often resemble flowing liquid (hence its name).

Masses of flowstone are also frequently seen near other similar formations, since the mechanism by which they are formed is basically the same. When a mass of flowstone creates or encounters an overhang, for example, it often forms many small stalactites at its lower edge.