头层皮是动物身上的皮，表面有原始的皮肤特征，毛孔、皮肤纹理清晰，由又密又薄的纤维层及与其紧密连在一起的稍疏松的过度层***同组成，具有良好的强度、弹性和工艺可塑性等特点。
二层皮不是牛身上的皮，是头层皮的边角料打碎后加入聚乙烯材料重新贴合而成，然后在表面进行化学材料喷涂或覆上PVC、PU薄膜制作而成，它仍然保持牛皮的特性，但耐穿性及强度则不如头层牛皮。
The first layer of leather is made from skin of animals with the features of the original skin, which is composed of dense and thin fibrage as well as transition layer closely connected with the fibrage, and skin texture and pore can be seen clearly. The leather is of high strength, good elasticity and good plasticity in craftsmanship and so on.
The second layer of leather is made from the material of fitted mixture of the offcuts of the first layer of leather broken into pieces and polyethylene rather than the skin of cows. Sprayed chemical materials and coated with PVC and PU thin-film, the second layer still retains the characristics of the skin of cows, but its durability and strength is less then that of the first layer.