A 48ml refill for the Feliway Diffuser - one vial lasts approximately 4 weeks and covers an area of up to 650 feet. When the vial in your diffuser runs out, simply purchase another Feliway 48ml diffuser refill and slot it into your existing diffuser. The Feliway Refill contains a synthetic feline facial pheromone, which helps to ease cat stress and make your cat feel calm and secure, and less stressed. Your cat naturally marks its territory - including furniture, walls and even your legs - using pheromones secreted from his or her face, and this in turn makes the cat feel safe and secure. Feliway mimics this hormone to create a sense of safety and well-being for your cat. The Feliway Diffuser plug-in gradually emits the pheromone to create a stable calming effect in the home environment. Eliminating stress will help eliminate undesirable cat behaviour such as spraying, scratching and aggression.