The HydroBak Hydration Backpack reportedly holds enough water (i.e., 50 ounces) to maintain one's fluid level over the course of 1-2 hours of outdoor work or recreational activities. Its external-fill reservoir can be refilled without having to remove the backpack. Other features include: closed-cell insulation and neoprene cover designed to keep the water cool (or warm) for hours, the 'Big Bite' valve to access the water, and an external zippered pocket for storing cell phone or other items.