This article reports on the influence of copper content and particle size on the tensile properties of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE) mixed with up to 25 vol.% Cu micro-particles and up to 5 vol.% Cu nano-particles, and on the influence of Cu micro-particle content on the dynamic mechanical properties of these polymers. This influence depends upon the extent of branching and crystallinity in the particular polymer. The copper micro-particles seemed to have a negligible influence on the tensile strength of LDPE and HDPE, while there was quite a significant reduction in tensile strength when LLDPE was used as matrix. The elongation at break generally decreased with increasing copper content, but the effect was more significant in the case of LDPE and HDPE. The tensile modulus generally increased with increasing Cu content, but the extent of increase was lower in the case of the more crystalline HDPE. The nano-copper containing samples showed comparable properties at equivalent Cu contents. The storage and loss moduli generally increased with increasing Cu. For all three polyethylenes the beta-transition (where present) was not significantly influenced by the presence and amount of copper, but the alpha-transition was strongly influenced, especially in the case of LDPE and LLDPE.