It is well known that cross-linking of polyethylene molecules into three-dimensional networks improves material properties; in particular, it enhances impact strength, thermal performance and chemical resistance. A product of good characteristics can be obtained if the manufacturing process is adequate and all involved machines are working properly. In this context, infrared thermography as a remote imaging technique may be a valuable tool to monitor the polyethylene cross-linking processes. Experimental tests were carried out on specimens without treatment and on specimens treated with either chemical processes or electron beam irradiation. Our results prove that lock-in thermography can detect local non-uniformity of material characteristics due to either the extrusion or cross-linking processes, and material differences linked to the different compound.