User blog comment:Unownshipper/Flora and Fauna of Rapture/@comment-6024608-20131019124102/@comment-71.155.150.228-20131020030425

Despite the nickname, the ony part of the pig used is its bladders to inflate the balls, which even back in Rapture's time, that was replaced by rubber or polyurethane bladders. The skin is mostly leather,( deer or cattle leather was commonly used), but any mammal skin would do.