Extrusion welding (also known as Injection Welding) is a variety of heat sealing in which a welding rod is preheated and applied to plastic pellets that act as a welding medium. This welding rod is then pushed against the molten plastic into or along a seam to create the bond. These methods are usually used on larger heavier gauge materials where the strongest possible weld is necessary for large tanks or high-capacity bladders.