How many different layers in a regular vinyl decal?

In a regular vinyl decal, there are 3 different layers.
The bottom one is a smooth paper. At the end, it is useless.
The middle one is the vinyl decal. It is the most important layer of the vinyl decal.
The top one is the paper/plastic mask. At the end, it is also useless.

A vinyl decal comes in where the vinyl decal is stick with the smooth paper. When you apply the paper/plastic mask on the top of the vinyl decal, the vinyl decal will stick with the paper/plastic mask. At that moment, the bottom smooth paper is useless. After you apply the vinyl decal with paper/plastic mask on a surface, the paper/plastic mask become useless as well.
Of course, you cannot apply the vinyl decal correctly without the smooth paper and paper/plastic mask.