Just like the beer koozie, Bladder Koozies insulate your Camelbak® reservoir or Hydration pack water bladder. These koozies help keep your water cool in the heat and prevent freezing in the winter. Insulate your water bladder reservoir before you put it in your pack or carrier.Camelbak 50 oz/1.5L MIL-SPEC Antidote Accessory Reservoir 90855*Empty Reservoir Dimensions: 11.5 x 7 in / (29.2 x 17.8 x 2.5 cm) *Full Reservoir Dimensions: 11 x 6 x 2.5 in / (27.9 x 15.2 x 6.4 cm)Look for Us on YouTube.