The Yin foam roller is a foam roller that massages and releases tension within the long muscles of the spinal column. The yin roller is 6in x 6in x 6in. The foam that is used is a medium density foam. the yin roller grabs at the fasciia and the muscles of the spinal column and is able to massage, twist and smooth out all of the built-up tension within the spinal column. The Yin roller is Stretch Therapy tested and approved. You receive instant tension release within the upper back, traps, neck, mid-back, thoracic area and the lower back. This style roller acts as a deep muscle hand twisting massage that grips the muscles and fascia throughout the length of the entire spine in order to penetrate those areas that traditional foam rollers cannot reach.