A wood plastics composite (WPC) is a term which refers to a composite material containing wood in any form, combined with either thermoplastic or thermoset resin.

Most WPCs currently on the market are made from thermoplastics, in particular high density polyethylene (HDPE). The nature of the wood content is either wood flour or sawdust. At first inspection, the combination of wood fibre and a thermoplastic does not seem promising. Wood fibres (eg in the form of sawdust) are short, tend to absorb moisture and are not strong when compared with either the glass or carbon fibres used in FRPs. Thermoplastics are much weaker than thermosetting resins, soften with increasing temperature and creep under load. However, WPCs combine inexpensive or waste raw materials, and the production process for low technology sections such as decking planks, fencing and handrails is relatively simple. Particularly in the USA, WPCs have been hugely successful because they offer advantages of durability and lower maintenance over natural wood. Solid recycled plastics lumber (RPL), is usually made from waste plastics without any wood or fibre element (and is therefore is not a composite), also competes in this non-structural role. Polyvinyl Chloride (PVC-U) is another type of plastics which has familiar application for window frames, doors and fascia panels.

Although very much more low-tech compared with the more advanced FRPs, WPCs are beginning to be used for structural applications. Developments such as fibre orientation and better coupling additives have already taken place. Although WPCs are generally weaker than timber, particularly in flexural stiffness, in many cases their structural performance will be adequate. The main advantage of WPCs is the resistance to decay, insect attack, warp and splintering.

Future development of WPCs for structural use may take the following form:
• Co-extrusion with reinforcing rods (either steel or FRP)
• Co-extrusion/pultrusion with longitudinal glass fibres (bundles, tapes or mats)
• Modification of the thermoplastic/wood fibre mix into stiffer, more resin-like materials
• Better bonding between matrix and fibre by advances in additive and cross-linking technologies

WPCs require fine ground, dry, clean sources of wood fibre. This is most likely going to be obtained from the wood working industry rather than from sawmills or from virgin timber such as forest thinnings. Increased recycling of waste plastics and wood waste, and developments in production processes, will decrease the price of WPCs and encourage usage. Two WPC manufacturers have recently started production in the UK.

WPCs will displace use of solid timber in both outdoor and indoor markets. Advanced FRPs also offer an alternative to timber for some engineering applications such as bridges, and are also beginning to be used for doors, window frames and cladding.