VENTILATED BACK SYSTEM
So that you don’t get too sweaty, many rucksacks have mesh panels that hold the sack away from the body to increase airflow and thereby reduce the horrid, clammy sensation that some rucksacks can cause. The greater the airflow across the back, the less clammy you will feel. Back systems without such airflow may be closer fitting, more stable and lighter. Those without open mesh foam don’t soak up rain or snowmelt so they do have advantages.