The Evolution Drop-in Air Bath Bathtub from American Standard provides a gentle massage using thousands of warm air bubbles. The Evolution air bathtub is the only air massage tub with our exclusive EverClean® molded directly into the air circulation components to inhibit the growth of mold and mildew in the pipes. This air bath tub features 24 smooth air jets, double-intensity lumbar massage, and variable speed heater for the ultimate in relaxation. This deep-soak tub allows for 3-in. of added water depth with the addition of overflow drain, sold separately.