oh no, no "substitute" is necessary. it's just a simple mix of baby shampoo and water. a while back there was a thread somewhere around here that talked about what to do when you run out of the initial bottle that the skins come with. when I ran out, just bought a little bottle of baby shampoo and shot a few drops into a wide bowl of water, and soaked the film in it before applying. the mixture the better. hope this helps.