Although cross-linked polyethylene is not very common, it is sometimes used for fuel tanks, kayaks, canoes, and older ATV parts. This extremely durable plastic is difficult to repair because it is a thermoset plastic, meaning it cannot be melted. The plastic identification symbols for cross-linked polyethylene include XPE, XLPE, PE-Xb, and PEX. If no symbol is present, the best way to determine if the polyethylene is cross-linked or thermoplastic is to test whether it melts. Thermoplastic polyethylene will melt easily, while cross-linked polyethylene will not; it may turn brown or become soft and flexible, but it will not melt.

Since cross-linked polyethylene is not meltable, a nitrogen plastic welder or airless plastic welder cannot be used for fusion welding. Instead, we used an airless plastic welder with a flat tip and flat low-density polyethylene (LDPE) welding rod to make a bonded repair to a puncture, crack, and hole in this cross-linked polyethylene fuel tank.