How a computer is constructed and what pieces go into the system are critical. EPEAT looks at the reduction and/or elimination of environmentally sensitive materials such as cadmium, lead, mercury, PVC, and other chemicals and metals. It also rates computers on the percentage of post-consumer recycled plastics as well as bio-based plastic materials used in the construction of computer components and how computers are packaged for delivery/sale (minimization of packaging and use of recycled content and ease of recycling packaging materials). EPEAT also rates the simplicity of upgrading and/or replacing components to help extend the useful life of computer systems.