Freeze and freeze-thaw durability characteristics of fiber reinforced polymer (FRP) composites, especially in the presence of moisture, need to be investigated prior to the widespread implementation of these materials in civil, polar, and offshore structural components and systems. The hygrothermal degradation characteristics of an ambient cure E-glass/vinylester system due to exposure to -10degreesC conditions and conditions of freeze-thaw, including in the presence of water and seawater, was investigated. Changes in mechanical characteristics such as strength and modulus, and thermo-mechanical dynamic characteristics such as storage and loss moduli, and glass-transition temperature were measured, and short-term effects of environmental exposure were assessed. It is seen that the presence of moisture/solution has a significant effect; both in terms of physical and chemical aging, and in terms of microcracking and fiber-matrix debond initiation. Results indicate the critical importance of cure characteristics and diffusion related phenomena.