Increased material flammability due to exposure to high oxygen concentrations is a concern from both safety and operational perspectives. Localized high oxygen concentrations can occur when exiting a higher oxygen concentration environment due to material saturation as well as oxygen entrapment between barrier materials. Understanding of oxygen diffusion and its correlation to flammability risks can reduce the likelihood of fires while improving procedures as NASA moves to longer missions with increased extravehicular activities in both spacecraft and off-Earth habitats. This paper examines the time required for common spacecraft materials exposed to oxygen to return to reduced flammability after removal from the increased oxygen concentration environment. Specifically, NASA-STD-6001A maximum oxygen concentration testing and ASTM Standard F1927 diffusion testing were performed on Nomex® HT90-40, Tiburon® surgical drape, cotton, Extravehicular Mobility Unit (EMU) Liquid-Cooled Ventilation Garment, EMU Thermal Comfort Undergarment, EMU Mosite foam with spandex covering, Advanced Crew Escape Suit (ACES) outer cross-section, ACES Liquid-Cooled Garment, ACES O₂ hose material, Minicel® polyethylene foam, Minicel® polyethylene foam with Nomex® covering, Pyrell polyurethane foam, and Zotek® F-30 foam.