hydration pack is a type of
hydration system built as a backpack or waistpack
containing a reservoir or "bladder" commonly made of rubber or
plastic. The reservoir contains a capped mouth for filling with liquid and
hose that allows the wearer to drink hands-free.
Most hoses end with a "bite valve" that opens when the user bites down on it; the valve may be protected by a dust cover.
Some hydration packs are insulated to keep water from freezing or becoming warm.
Reservoir sizes commonly range from 1.5 to 3.0 litres.
Hydration packs are commonly used for outdoor recreational activities,
such as hiking, bicycling, and kayaking, as well as for military
They are also quite popular at Burning Man, where the combination of storage and ready hydration is useful due to the dry conditions on the playa.