Check the listing for details. Feliway Optimum Diffuser Refill for Cats, 48 ml. - UPC: 850002593129 exp 10/26. Condition: New. Listed at 13.00 USD. Keep your cat calm and comfortable with Feliway Optimum Diffuser Refill. This 48 ml refill is specifically designed for cats and is suitable for use in any home. It helps to reduce stress and anxiety in cats by mimicking the pheromones that cats produce naturally. The refill is easy to use and can be plugged in anywhere, making it perfect for travel or for use in multiple rooms. It's also long-lasting, with an expiration date of 2026, so you can be sure that your cat will stay calm and comfortable for a long time.