The Chill-Its 5050B Two-Liter Replacement Bladder is compatible with the 5155 Hydration Pack (sold separately). The bladder features a DualCap for easy no-spill filling with water or ice, plus an insulated tube to keep water cool in the heat. Capacity: 2 L. For Use With: ergodyne Chill-Its 5155 Hydration Packs; Color(s): Blue; Color Family: Blue; Material(s): Thermoplastic.