NOW Foods - BPA Free Glass Swirl USB Diffuser NOW Ultrasonic Glass Swirl USB Oil Diffuser unites scientific innovation with the timeless tradition of aromatherapy to create a BPA-free diffuser that uses only tap water and your favorite essential oils. Instead of heat this contemporary diffuser utilizes high frequency ultrasonic electrical vibrations to create an ultra-fine mist which helps to maintain essential oil integrity and holistic properties.