Abstract: A waterproof zip closure is formed by extruding a first thermoplastic material onto its teeth, and applying a transverse force while the first thermoplastic material cures. The transverse force is sufficient to move the teeth in the separating direction, but is less than that which can cause separation. After curing of the thermoplastic material, the tapes and teeth of the zip closure are coated with a second thermoplastic sealing material, while the transverse force is maintained. When the transverse force is removed the sealing material is forced together to provide a waterproof seal. The second thermoplastic sealing material on the tapes further improves the waterproof nature of the zip closure.