Commercial breathing-air devices contain gases that may vary in concentration from 20.9 percent to 100 percent oxygen at pressures up to 34.5 megapascal (MPa). Analysis of the limited flammability and reactivity data available on some of the materials in these devices under use conditions raised serious concerns about the risks to National Aeronautics and Space Administration (NASA) and contractor personnel at the John F. Kennedy Space Center (KSC). Therefore, these materials were evaluated using the criteria of the ASTM Test Method for Autogenous Ignition Temperature of Liquids and Solids in a High-Pressure Oxygen-Enriched Environment (G 72), ASTM Test Method for Determining Ignition Sensitivity of Materials to Mechanical Impact in Ambient Liquid Oxygen and Pressurized Liquid and Gaseous Oxygen Environments (G 86), ASTM Test Method for Heat of Combustion of Liquid Hydrocarbon Fuels by Bomb Calorimeter (D 240), and Flammability, Odor, Offgassing, and Compatibility Requirements and Test Procedures for Materials in Environments that Support Combustion (NASA-STD-6001), Test 1, Upward Flame Propagation. Materials typically used in these devices that do not meet the KSC requirements include: polyethylene, Delrin®, Neoprene®, Buna N®, Zytel 42®, ethylene/propylene rubber (EPDM), Tefzel®, Noryl®, Buna S®, and silicone rubber. Comparative data were also generated on Teflon TFE®, Viton A®, Vespel SP-21®, and Kel-F 81®. In mechanical impact tests, polyethylene, Buna N®, Neoprene®, and Zytel 42® passed at higher than expected energy levels while Tefzel® reacted similar to Delrin®. In the autoignition tests (AIT), the AIT for Buna N®, Neoprene®, ethylene/propylene rubber (EPDM), Buna S®, Delrin®, Tefzel®, Viton A®, and Zytel 42® decreased with increasing oxygen concentrations while the effect of oxygen concentration was minimal for Teflon TFE®, Kel-F 81®, Vespel SP-21®, polyethylene, and silicone. The heats of combustion ranged from 6.17 megajoule per kilogram (MJ/kg) for Kel-F 81® to 54.59 MJ/kg for polyethylene. All materials failed the upward flammability test in 20.9 percent oxygen except Teflon TFE®, silicone, Zytel 42®, Viton A®, and Kel-F 81®.