Smooth vs. Textured Linings

Why is the interior lining of my classic flap more textured and rougher compared to the smooth lining of my other one?

Because of texture!

The difference in texture is due to the type of hide used for the lining. If the lining is made of sheepskin, it will feel more textured and rough because the grains or follicles are larger and sit lower than the surface of the hide. In contrast, if the lining is made of lambskin, the grains are tiny and on the same level as the hide, resulting in a smoother feel. When you run your hand over sheepskin, you’ll notice the texture variations between the raised areas and the recessed follicles, whereas lambskin feels uniformly smooth because both the grains and the hide surface are at the same level.