1.1 This test method covers the determination of the coefficient of linear thermal expansion for plastic lumber and plastic lumber shapes to two significant figures. The determination is made by taking measurements with a caliper at three discrete temperatures. At the test temperatures and under the stresses imposed, the plastic lumber shall have a negligible creep or elastic strain rate, or both, insofar as these properties would significantly affect the accuracy of the measurements. 1.1.1 This test method details the determination of the linear coefficient of thermal expansion of plastic lumber and plastic lumber shapes in their “as manufactured” form. As such, this is a test method for evaluating the properties of plastic lumber or shapes as a product and not a material property test method. 1.2 The thermal expansion of plastic lumber and shapes is composed of a reversible component on which it is possible to superimpose changes in length due to changes in moisture content, curing, loss of plasticizer or solvents, release of stresses, phase changes, voids, inclusions, and other factors. This test method is intended to determine the coefficient of linear thermal expansion under the exclusion of non-linear factors as far as possible. In general, it will not be possible to exclude the effect of these factors completely. For this reason, the test method can be expected to give a reasonable approximation but not necessarily precise determination of the linear coefficient of thermal expansion. 1.3 Plastic lumber and plastic lumber shapes are currently made predominately with recycled plastics where the product is non-homogeneous in the cross-section. However, it is possible that this test method will also be applicable to similar manufactured plastic products made from virgin resins or other plastic composite materials.