Class I: Titanium dioxide dry milled and untreated, Class I titanium dioxide has a low surface area and low oil absorption.

Class II: Class I titanium dioxide is treated and wet milled to remove large particles and coated with 4% amount of silicon-aluminum. It has the lowest surface area and the lowest oil absorption.

Class III: Typical superfine coating grades with organic coating.

Class IV: Large coating amount, which can be further divided into IVa and IVb. The coating amount is between 5 and 10%. IVb is mainly used in titanium dioxide with high added amount, because its opacity is better than IVa.