Perhaps one of the most important advancements to the industry is the 3D roller. 2D rollers move back and forth along the X-Y plane (back and forth + up and down) while the 3D roller actually protrudes intothe body from 2.2 inches to 5 inches closely mimicking the feel of human hands. With a 3D roller, you are able to enjoy a much deeper tissue massage than ever before possible from a massage chair. 4D massage chairs take this experience to an entirely new level with speed variation and more control. http://www.dodochair.com/3d-massage-chairs/