Light stabilizers & UV absorbers HALS as HATS HALS as HATS While originally introduced as highly efficient light stabilizers, Sterically Hindered Amine (HAS) have also been found to be very efficient thermal stabilizers in polyolefins. As HAS work by scavenging both oxygen centered and carbon centered radicals [see Figure 1], , they should work independently from the initial radical source - UV radiation or thermal stress. Figure 1: Cyclic process - HAS regeneration The effect of HAS as thermal stabilizers was not initially realized because accelerated oven aging testing was done as close as possible to the melt temperature of the polymer in order to accelerate test results. The effect of HAS as thermal stabilizers is most evident when testing is done closer to actual use temperatures.