Whether you39re commuting in the rain or canyoning down a waterfall this is a fully featured waterproof backpack that will protect your gear from the elementswhat size do i needthe backpack has a 25 litre capacity this is enough to carry a 17quot laptop a change of clothes and a small lunchthe external mesh pockets will each hold a 2l water bottle magazine or tripodthe lashtabs on each chest strap and main bag are enough to carabiner on a bicycle helmet or pouchkey featuresfull size