The dual membrane gas trap filter is utilized in the internal thermal control system (ITCS) as part of the pump package assembly to remove non-condensed gases from the ITCS coolant. This improves pump performance and prevents pump cavitation. The gas trap also provides the capability to vent air that is Ingested into the ITCS during routine maintenance and replacement of the International Space Station (ISS) system orbital replacement units.The gas trap is composed of two types of membranes that are formed into a cylindrical module and then encased within a titanium housing. The non-condensed gas that is captured is then allowed to escape through a vent tube in the gas trap housing. The gas trap requirements include the ability to remove gas bubbles from the ITCS coolant water and maintain an outlet gas concentration less than 0.5 percent by volume, a pressure drop of less than 34 Pa (5.0 psid) at 1360 kg/hr (3000 Ib/hr) without water leakage, a 620-Pa (90-psid) proof pressure, and a 1-KPa (150-psid) burst pressure capability.This paper describes the principles involved in the gas trap design and the development of the current mature design that will be utilized on the ISS. The performance capabilities and the operational lifetime of the unit will also be discussed. Test data validating gas trap performance will be presented to demonstrate gas removal capability versus time, maximum gas removal capacity, and the sensitivity of the ITCS gas trap to water contamination when it is exposed to an ethanol/water mixture.