This is our special system of injecting foam into the lure body, which creates extra strength in the lure body, but also means in the unlikely event of a huge fish puncturing the outer HD ABS plastic body, the lure will still function perfectly and still float and swim with the same great action it was designed with. In areas with mackerel, barracuda, cubera snapper orwahoo, this system means that lure failure is not going to happen.