Heat Deflection Temperature (HDT) of plastics

Heat deflection temperature (HDT), also known as heat distortion temperature, describes the plastic's resistance to deformation by a given load at an elevated temperature. It can also give insight into the injection mouldability of the plastic.

HDT is defined as the temperature where the sample specimen bends 0.25 mm under a given weight. It 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 are chosen according to the tested material. The test is always done as a duplicate.