Heat Deflection Temperature (HDT) of plastics

Heat deflection temperature (HDT) is a measure of a plastic's resistance to deformation at a given load at an elevated temperature. It is defined as the temperature where the sample specimen will bend 0.25 mm under given weight. It is useful, for example, in evaluating how easy the plastic is to the machine and to resist deformation due to temperature. It can also give insight into the injection mouldability of the plastic. HDT can be measured with either method A (1.80 MPa), B (0.45 MPa) or C (8.00 MPa) as per ISO 75. The load and specimen type is chosen according to the tested material. The test is always done as a duplicate.