Humidity control is essential in the extravehicular mobility unit (EMU). Excessive humidity can lead to visor fogging; accumulation of water, which can block air flow through the vent loop and corrode system components; and uncomfortable conditions for the person inside the EMU, reducing productivity.This paper describes the development of a membrane-based process for dehumidifying the EMU. The membrane process promises to be smaller, lighter, and more energy efficient than the other technologies being considered for dehumidification, and it requires no expendables. The system employs novel dehydration membranes, which were tested for 90 days at conditions expected to be present in the EMU. The results of these tests indicate that membrane-based technology can effectively control humidity in the EMU.