The Boomerang Roller with Surface Skin Technology (SST) is a part of the Addaday and Robert Forster P.T. collaboration. The roller contours around the body allowing it to reach hard-to-get to areas like the back and shoulders. The direction of the rollers also allow for great Cross Fiber Friction Massages. The Boomerang has 2 different density gears, one with SST and the other without SST for a harder massage. The SST on the Boomerang is our medium density version.