the welding rod is a laminate structure in which a print layer is disposed between a first thermoplastic layer and a second transparent thermoplastic layer . preferably the welding rod is in the form of an elongated element having a half - round cross - sectional shape . the welding rod is used to join two pieces of thermoplastic sheeting , particularly flooring , together . if the welding rod has a pattern similar to the printed pattern of the sheeting the resulting surface covering looks seamless .