The skin gives the part its form and stiffness, while the cellular core contributes to the very high strength-to-weight values of the material. These are higher than those of some unfoamed plastics and metals. The sandwich-like structure with its unique mechanical properties was prompted by nature. Wood and bone are strong and light-weight natural materials having a cellular structure. Since the sandwich-like structure of the integral foams resembles that of natural wood, the foams are often referred to as artifical wood or plastic wood, thereby emphasizing not only the formal structural similarity of these materials, but also one of the main functional applications of integral foams - replacement of wooden articles in various fields of engineering and construction.