Currently, ASTM D7031 – Standard Guide for Evaluating Mechanical and Physical Properties of Wood-Plastic Composite Products states that the distinction between wood-plastic composites and “plastic lumber” is that a wood-plastic composite must contain less than 50 % plastic resin by weight (using an oven-dry basis for the wood fiber content).

The standard for determining design values for wood-plastic composites was developed by ASTM Committee D07 and is designated ASTM Test Method D7031-11 Standard Test Methods for Evaluating the Mechanical and Physical Properties of Wood-Plastic Composite Products.

There are several standards for determining design values for plastic lumber developed by ASTM Committee D20. Those standards should be consulted for information on plastic lumber.