Can you use composite decking for fencing?

While composite decking can be used for fencing simply because it is an exterior dimensional board, it is not recommended to use composite decking as a fence because manufacturers do not design their boards for such an application. Composite decking boards are quite pliable and tend to sag over long spans. Trex manufactures a composite fencing system that uses the same material as its composite decking but has been designed specifically for fencing applications. Trex Decking boards are the best composite materials for walking surfaces, but the Trex Seclusions fence system was designed specifically to serve the function of a privacy fence. By using the decking in place of the fencing, you are sacrificing many of the benefits that Trex Fencing offers, such as the full privacy, the neighbor friendly look, and the beautiful cap and trim design. Trex has been manufacturing fencing since 2005 and the product is available for shipment nationwide. 

Check out https://www.trexfencingfds.com/why-trex/virtues-and-benefits/ for more information regarding the virtues and benefits of Trex Fencing.