HOP BAG Anti-shock System Spring and air-cushion combination aids in relieving user of backstress and provides spring motion that gives user to add push when hiking or walking. Our highly dependable and tested anti shock when inuse. This feature helps ease the weight by more than 30% of time. Ventilation System Air padding construction provides space for venitilation.Backing material made of mesh for better air fiow and dissipates heat from the back of the user.