The collar incorporates a patented insecticide-release technology. Friction releases the insecticide deltamethrin steadily onto the dog’s skin over 6 months. Contains Deltamethrin 4.0%. Water-resistant: can be worn while swimming or bathing without impairing effectiveness. For use on dogs and puppies over twelve weeks of age. One size fits all. Includes two collars in every resealable tin so your pet is covered for up to 12 months.