Napa is the upper side of the leather hide, simply expressed the hair side. The surface structure / grain differs between various leather hides.
Lamb napa: Is thin and supple, the surface structure is even and
smooth. Lamb / sheep makes for light and soft garments.
Pig napa: Is thin and strong, distinguishing features are small
holes which can be seen along on the surface structure.
Goat napa: Is strong and elastic in all leather.
The surface structure has a distinct pattern.
Cow napa: Strong and has a tight firm feeling.
The surface structure is smooth with a slight pattern.