Nap fabrics have a definite surface texture and must be cut in one direction. If the fabric is not cut correctly it will look like the garment has been made out of different color fabrics.
Corduroys and velvets have a raised nap that you can feel by running your hand along the surface. Rub your hand in one direction and it will feel like you are rubbing an animal's fur in the wrong direction. Rub the fabric the other way and it will feel like you are stroking the animal in the right direction. Just like stroking the animal from top to bottom, the fabric nap should run from the top of the garment down to the bottom. Once the direction of the nap has been determined, the pattern pieces can then be laid out. The example below shows the correct way to lay out pattern pieces with a nap.