Polyolefins are increasingly used in the construction of lightweight structures. Due to their low surface energy, it is difficult to have a proper bond with adhesives and paints. By using cold plasma treatments, these surfaces can be activated through the formation of highly reactive functional groups that can promote high strength adhesive bonds. This paper compares the results of cold plasma treatments using two techniques (low pressure and atmospheric plasma torch) applied on polypropylene and high density polyethylene. The obtained data allow the demonstration of a higher effectiveness of atmospheric plasma, with a significant increase in surface energy in both materials.