The 2 layer construction of the AcoustaGrip Protege Charcoal is a key feature. The 1st layer consists of our custom designed and produced acoustical materials, delivering superior sound and extreme comfort. The 2nd layer is unique as it attaches simply with air to the back of your instrument. Because it attaches with no glues or clamps, AcoustaGrip helps to preserve and protect the quality of your violin or viola. Because AcoustaGrip is ergonomically designed and so comfortable, your little one can focus all of their attention on honing their technique and playing more expressively without being distracted by the constant physical pain that all too often accompanies playing with a traditional shoulder rest.