This paper will present a study comparing the chest response of the Humanetics Innovative Solutions Incorporated (HIS) Hybrid III 5 th Percentile harmonized dummy with that of the Denton ATD (DN) and First Technology Safety Systems (FTSS) 5 th percentile dummies. This study focuses specificallyb on the differences in the chest jacket designs, comparing the harmonized chest jacket used on the HIS dummy developed through the SAE technical working group in 2009 that was formed to address differences between the chest jackets of the two dummy brands at the time;​ Denton and FTSS chest jackets. The authors will present data from chest impact tests conducted in accordance with Part 572.134 Thorax impact. Additionally data will be presented for chest impacts conducted in accordance with SAE J2878. This test method produces chest deflections which are more inline with the deflection amounts typically seen in full scale vehicle testing conducted in the US New Car Assessment Program (NCAP). Additionally, controlled sled testing was conducted to compare the response observed in the chest impact testing to the chest deflections generated during seatbelt loading. For the sled test a 8 g 1⁄2 sine wave pulse with a duration of 175 msec. was selected, again, because it generated chest deflection amounts typically seen in the U.S. NCAP 35 mph frontal barrier test (15~20mm). Additionally, three belt positions were used to study the chest response for the three chest jackets depending on belt placement;​ a nominal position as well the shoulder belt position shifted 50 mm inboard and 50 mm outboard. All three dummies fell within the corridors of the Part 572.134 chest impacts required for FMVSS 208 with harmonized dummy having slightly less deflection 50 mm versus 51 and 52 mm for the FTSS and Denton dummies respectively. Chest impacts conducted per SAE J2878 showed the same tendency as Part 572.134 chest impacts with the harmonized dummy again showing slightly lower deflections than the FTSS and Denton dummies. Sled testing results showed the same tendencies as the chest impact tests with the HIS dummy with the harmonized chest jacket showing ~2mm lower chest deflection than the FTSS and DN dummies. It was also noted that the deflection amounts for all three dummies tend to be very sensitive to belt placement. Specifically, the deflection tended to be less if the belt remains on one of the dummy’s breasts for the duration of the test;​ compared to cases where belt slips off the breast during the loading.