To meet the energy and space requirements of today's building market, builders are looking for new materials and practices to insulate their walls. Vacuum insulation panels (VIPs) have shown potential to meet or exceed today's high insulating levels while keeping the thickness of the building envelope down. One of the problems facing owners and builders wanting to use VIPs is their unknown service life. Recent research has focused on developing methods to accelerate ageing in order to determine the service life of VIPs. However, a disconnect exists between results obtained from accelerated ageing and real time degradation (due to moisture accumulation). To study the effect of moisture on thermal performance, VIPs from two manufacturers were held in a climate chamber at 30 and 90% relative humidity for 30 days. The panels tested saw a mass increase of 0.05% and 0.2% and a thermal resistance decrease of 5% and 6.5%, respectively.