RAGOL BENTONITE is a common name for the anionic smectite clay minerals used by paper makers as a retention and drainage additive or "microparticle." Under the scanning electron microscope (SEM), bentonite particles can be almost indistinguishable from kaolin filler clay or coating clay. The main difference is the thickness. The sodium or potassium salts of bentonite exfoliate into extremely thin plates. In theory these plates can be as little as about 1 nm in thickness, yielding a huge surface area per unit mass. In practice, not all of the platelets will become separated from each other.