Ion exchange membranes are a promising class of materials for use in fuel cells, barrier layers, and water splitting devices. While the majority of research related to anion exchange membranes is on improving the chemical stability and increasing ionic conductivity, themechanical performance under relevant operating conditions is vital to device lifetime. Using tensile testing and humidity cycling, we report the mechanical performance of Nafion 115, polyethylene-b-polyvinyl benzyl trimethylammonium diblock copolymer (PE-b-PVBTMA), poly[t-butyl styrene-b-hydrogenated isoprene-b-vinyl benzyl trimethylammonium-b-hydrogenated isoprene-b-t-butyl styrene] (QP43), and aminated tetramethyl polyphenylene (ATMPP). Nafion 115 serves as a well-studied material to compare with the developmental anion exchange membranes. A home-built environmental chamber attached to a rheometer was utilized to perform all measurements under elevated temperature and relative humidity conditions. Standard mechanical properties are important to understanding membrane performance, but a simple metric comparing the mechanical elongation in a dry condition with the in-plane swelling percentage in liquid water can be used to predict how membranes will perform under hygral cycling. (C) The Author(s) 2016. Published by ECS. All rights reserved.