Kool Collar Kool Tube Refill Pack Medium (17 1/2"-24") Large (24"-30 1/2")Keep your pet cool, safe & comfortable...How it works: Cycle extra KoolTubes inside KoolCollar for constant cooling.What it does: Promotes comfort & reduces heat related health problems.When & Where to use: Use indoors with KoolCollar year-round. Use at home, in the car, motorhome, anywhere!KoolTubes are intended to be used anytime it's not practical to have your dog dripping water from using ice in the KoolCollar. Each KoolTube usually lasts about 30-50 minutes depending on the ambient temp, the dog's body heat and activity level. KoolTubes should not be used outdoors. The cooling energy is enough to "take the edge off" in a reasonable indoor temps, but not enough to thoroughly cool your dog outdoors.Reusable & Non-toxic Vet recommended