The support. If air is introduced as part of the support, either it needs to be filled very hard (which is basically the method of Tesla mattress) Or the pressure point support is not enough due to the movement of air, which is easy to feel the floor. Compared with inflatable mattresses, people are more accustomed to and prefer the feeling of sponge mattresses. The surface has a soft depression, and the bottom has enough support, which is why we choose sponge Slope. There is a 3.2in drop when the rear seats are folded down, and the sponge thickness needs to be larger than the drop to eliminate the feeling of slope. After our testing, 4.5in is the best thickness, which does not occupy vertical space and can be compressed and placed in the front and rear of the car Size.