The Freedog Cool Pro Tech blue collar has been specially designed to provide your dog with maximum comfort even on hot days. It is equipped with an integrated gel that ensures your furry friend stays pleasantly cool on warm days. Additionally, a special fabric has been incorporated that changes its pattern when wet, clearly indicating when the cooling function is active., , Here's how it works: Wet the collar with water. Once the pattern appears, the collar provides a cooling function., , , Product Information, , Innovative collar, Active cooling through water, For hot summer days, , Sizes:, , Length / Width in cm, , S: 20 – 42 / 1.5, M: 43 – 52 / 2.0, L: 53 – 63 / 2.5, , The length refers to your dog's neck circumference.