We'd rather wear our hydration instead of carry it, which is why we like the Patagonia Slope Runner 4L Vest. With its low profile fit, the Slope Runner wears more like a shirt than a pack as it carries our water or energy drinks close to our body for more comfortable, bounce-free running. The front stretch mesh pockets carry two 500mm flasks (included) while the zippered back panel can accommodate a hydration reservoir or stash our jacket out of our way until we need it. To maintain a performance fit, this vest features an adjustable inner harness with load-lifting bungees on the top and sides to balance our load and adjust our carriage on the go as we're flying down the trail or slopes.