Polypropylene Decking Materials
Though polypropylene is also found in composite decking materials, when a deck board is made entirely from polypropylene, you won’t find any organic composites in the mix. Polypropylene decking materials are created using a plastic-extrusion process. The boards are lighter than composite decking, but have a shinier appearance, looking just like plastic. White vinyl fencing material is also made from polypropylene.
Polyethylene Decking
Polyethylene deck materials, often reclaimed from recycling bins, include organic materials with inorganic materials to form deck boards. These wood-plastics are made from many different plastics or polymers -- polypropylene, polyethylene or polyvinyl chloride. They are then combined with wood bits ground to the consistency of flour and bonded together with additives and adhesives to make the board.
Differences
Both materials have their disadvantages and advantages. Both products cost more than wood, but may cost less in the end because there is no maintenance involved once decks are in place. Polypropylene boards are stiffer and can span joists 24 inches-on-center, whereas polyethylene composite deck boards require joists 16 inches-on-center. One drawback to using wood-plastic polyethylene composite boards is that these boards attract mold, fungi and mildew, but plastic polypropylene boards, having no organic materials, do not.
Weathering
The differences between the board types are most apparent when it comes to weathering. Plastic boards are affected by variations in extreme temperatures, especially when the variations span 100 degrees. A 10-foot board, for example, can contract and expand one-half inch in these weather changes. Wood-plastic composites, however, don’t suffer extreme contraction and expansion, but are affected by weathering and surface oxidization -- which means fading. Weather conditions, budget and architectural statements may be the deciding factors in choosing between all-plastic and wood-plastic composites when planning your next deck.