400 ml. The flip bag is a fitness tool. Long-term sedentary people, such as students, civil servants, it personnel, office administrators, etc. When resting, pat a certain part of the body with the racket bag flexibly and rhythmically. Through the principle of nerve reflex and meridian induction, it achieves the functions of dredging meridians, promoting qi and blood circulation, removing blood stasis and resolving hard mass, strengthening tendons and bones, preventing diseases and strengthening the body. Just use a 400 ml flip bag.