The Royal Australian Navy is to replace its existing minehunters with a new class of vessel entirely constructed from a glass reinforced plastic/foam sandwich composite. Previous studies have shown that structural properties of the hull composite are largely dependent on the physical properties of the foam core material and therefore thermally induced foam degradation could seriously impair the structural integrity of the vessel. Consideration of the Australian climate, and in particular that of the tropical North, led to evaluations of the temperature dependence of core properties. Results of tests on a number of commercially available modified PVC foams are presented.