Adjustable air bag part and backrest device

The utility model relates to the technical field of seat back supporting, in particular to an adjustable air bag part and a backrest device. The adjustable air bag part comprises an air bag body, an air bag, an inflation tube, an inflation ball and a one-way deflation valve, the air bag is arranged in a containing cavity of the air bag body, the air bag can be inflated through the inflation ball, the air bag can be deflated through the one-way deflation valve, when the adjustable air bag part is installed, a back plate sleeve does not need to be specially arranged for fixing the air bag, and cost is saved; the assembly difficulty is reduced. The backrest device comprises the adjustable air bag part, the adjustable air bag part can be fixedly connected with components of the backrest device through the connecting part, the limit distance between the supporting plate and the back plate can be adjusted, a back plate sleeve does not need to be specially arranged for fixing the air bag, and the overall assembly is