This paper describes our investigation of the effects of forced air plasma treatment on polypropylene and polyethylene. The morphology of the treated surfaces has been carefully examined using a variety of tools including optical profiling. The complex surface morphology was observed to change with increasing treatment and varying intensity of the treatment over the surface. Optimum treatment conditions have been deduced using surface energy determinations and can be compared with the morphological changes. Determinations of surface energy, both the polar and non-polar components, have been made after exposure to varying moisture conditions for varying times. Different results are obtained for different environments and from different materials. These results demonstrate that forced air plasma treatment is a highly effective means of increasing the surface energy of polymers, which can be long-lasting, provided the treated surfaces are kept in dry conditions.