I have no idea what they use, but things that put pressure on the arch area of the shoe, (like stepping up on a curb, where the curb digs into the arch area) with snap plastic ones and cause a squeak. During a resole a cable can fix the issue. On the other hand sometimes they have an unknown origin. I had a pair of G&G's that always had a squeak and even resoling did nothing to help the problem. It was incredibly annoying.