Often called Thin Skin, Scud Back or Nymph Back. Our is designed specifically for shell backs on scuds, sow bugs, shrimp and nymphs. Semperfli Bug Shell Back Thin Skin is a flexible clear 6mm or 1/4″ (in old money!) wide stretch material ideal for using on various shrimps, nymphs, scuds, wet flies, saltwater etc. It comes in approx 1.5m or 5′ lengths making over 150 shrimps or hundreds of nymph backs!