Deflection Temperature Under Load. The heat/temperature at which a specimen of material deflects or bends under a certain load. The ASTM D-648 test method covers DTUL tests with standard loads of 66 psi (455 KPa) and 264 psi (1,820 KPa) and measures the temp. at which a material deflects 0.01 inches (0.254 mm) under those loads.