Randoseru(Backpack) & Drowning accident

A Randoseru(backpack) tries to protect those who are carrying the Randoseru(backpack) on their back.
Ｆｉｒｓｔ, the thickness of a backpack eases the shock from the back received suddenly.
In any case,when it falls to a waterway or a deep puddle, a backpack becomes instead of an air bladder

Experience of the buoyancy　　　

                                   The source : yu-kan daily Web