Yup. For a lot of cats the layers are oil, undercoat, main coat. The undercoat is a very short, dense and wiry coat of fur to stop things getting from the main coat to the skin.

The undercoat, as you can imagine, also absorbs a lot of the oil. Most people who are allergic to cats are actually allergic to the oil.

Also, in very specific breeds, there can be 3 layers of fur (like Siberian, for example).