basically the backings are just to make the back a uniform surface, to help keep splinters from lifting. materials like fiberglass are strong, being used in laminate bows as a part of the equation which gives the bowyer any given weight.used on wood like red oak it is too strong and overpowers the wood underneath it. this is why most use paper,burlap, hickory,rawhide, silk, etc. out of all of these silk is very strong , but at the same time it isnt as thick as fiberglass so it wont overpower the wood.