In flight, aircrafts experience sub-freezing temperatures, whereas on the ground they experience higher temperatures. This repetitive temperature cycling leads to the environmental degradation of fibre-reinforced polymer composites used in modern aircraft as structural components. Damage due to effects of such environmental cycling experienced over an aircraft’s service life can be characterized by monitoring changes in dielectric properties as a result of chemical and physical changes in the states of bound and free water within the matrix of moisture-contaminated polymer composites. The relative permittivity of the composite is a function of the amount of water and nature of its interaction with the polymer network. Water forms bonds with the polymer network with varying degrees of restriction to dipolar rotation in an electromagnetic field, from firmly bound hydrogen bonding to loosely bound van der Waals attraction, to unconstrained “free” water in micro-voids. The degree of restriction to dipolar rotation with an electromagnetic field determines its amount of contribution to the bulk relative permittivity of the moisture contaminated polymer composite. In this study, 4-ply Style 7781 glass fiber/epoxy laminate 25 x 65mm samples at 0.25% and 0.40% moisture concentration were exposed to freeze-thaw cycles between +7℃ and -7℃ simulating aircraft temperature cycling, while the dielectric properties were continuously monitored using a 10 GHz split post dielectric resonator coupled with a vector network analyzer. Results show a continuous increase in relative permittivity with number of freeze-thaw cycles. This indicates increases in free volume occupied by bulk water in micro-voids within the polymer network on each freeze cycle due to expansion of liquid water when frozen. Water with preference for the free state is pulled into this new free volume causing a redistribution of free and bound water, and an increase in the amount of free-higher permittivity bulk water.