DTTD is Titanium Dioxide which has been surface treated with Dimethicone. If you are working with silicone oil formulations, it is particularly easy to mix in, without a lot of fussiness. It also has good water repelling qualities, a smooth and soft skin feel (not draggy), good adhesion, high compressibility and spreadability.
Here are some recipes we created for testing in a matte liquid lipstick line.