Slide the refill into the case before attaching it to the air conditioning vent. The Car Diffuser utilises the natural air flow in the vehicle to release fragrance but for more active diffusion, use it in conjunction with your car’s air conditioning. If you’re not planning on using the car for a while, place the refill back into the heat seal to keep the fragrance fresh. Each scent refill lasts approximately 3 months when opened and up to 18 months unopened.