Minimalist ultra-light hydration pack for the final ascent or reservoir sleeve to throw in a larger multi-day pack - you get both with the Arete 18. Convert the Arete into a reservoir sleeve and place in your larger pack to be your hydration solution as you trek to basecamp. When you're ready to go for the summit, convert it back to its pack form and pack your summit essentials. The 2 liter Antidote hydration system also folds into its own pint-size pouch so you can throw it in a suitcase or stash it in your backpack. However you use it, the Arete 18 is a pack that will come in handy wherever you go.