The first major category is the soft shell, the main material has silicone, TPU, rubber. Good plasticity, the main thoroughfare is to prevent fall, earthquake.
The second category is characterized by a hard shell, the main material is plastic, resin, metal alloy. such as plastic shells, cell phone borders, and so on, anti-fall seismic function is relatively weak, can be ornamental relatively strong.
The third category is the leather cover, all kinds of pu leather, leather, artificial leather. Grade quality is different.