Trex is one brand of composite deckng made from wood flour and polyethylene and minor ingredients that give it better weather and sun resistance. The material is extruded into deck boards. It will last longer than wood. The brand I like best is made by Louisiana Pacific and is called weatherbest http://www.lpcorp.com/products/products_group.jsp?ProductGroupID=17
It uses virgin wood and polyethylene rather than recycled and the quality and appearance are higher.