For versatile and convenient hydration on our long-distance runs, we slip into the Salomon Active Skin 12L Hydration Vest, cinch it snug, and hit the trail. This vest-style hydration pack has a secure, close-to-body fit, and it lets us choose between a water reservoir in back (sold separately) or the two half-liter flasks in front (included). The stretch mesh maintains plenty of air circulation to keep us comfortable and plenty of adjustment points for a secure fit that doesn't bounce or rub as chase our PB and rack up the miles. On top of the versatile fluid storage, we also enjoy the zippered and stretch pockets to stash our snacks, gels, and optional jacket to gear up for the long haul.