Wood-fiber (WF) filled plastic composites (WPC) have gained rapid growth in recent years. Such materials offer significant advantages, which justify their use. Wood fiber is obtained from natural resources, it is available in various forms in large quantities, light, cheap, and it can be added to commodity matrices in considerable amounts thus offering economically advantageous solutions [1–4]. The main drawbacks of such composites are their poor adhesion to basically all matrix polymers [5, 6] and high density compared to natural wood and certain plastics [7].