The two-layer design of the AcoustaGrip Protege Charcoal is a key feature. One layer is made from special acoustical materials, delivering enhanced sound and ultimate comfort. The other layer is unique as it attaches simply with air to the back of your instrument using micro-air technology. Its ergonomic design sets the violins position at the most favored angle for sound projection and ease of performance. No more sores, marks or shoulder pain.The Protege Charcoal attaches with no glues or clamps, helping to preserve and protect the quality and condition of the violin or viola. The 1697 Napoleon Stradivarius and the 1778 DeLay Guadagnini enjoyed AcoustaGrip for many years. Both instruments were acclaimed for their condition and set world record sales prices.