Well, gelatin and water will not stick to Acetate or to Estar. So, you must make the surface of the transparent support, which is water repellant, non-repellant. To do this, you first apply a mixed water/organic mix to the support, or you bombard it with an electrostatic discharge to give it a "tooth" that is able to allow adhesion between the emulsion layer and the film. The organic/water mix is sometimes acetic acid, methanol and gelatin. This type of subbing will not work well on Estar.
If you apply a mixed water/organic mix, you are putting on a subbing layer. Then you coat your product on top. Some films are bombarded and subbed both and some films are just bombarded and coated with emulsion, so there are 3 possible coatings that can result. They are Subbed, Bombarded and Subbed, and Bombarded only. Any of these 3 can be coated on, but if the latter means is used, the Bombardment only method fades over about 24 hours.
More than you ever wanted to know I'll bet!