Microclimate packages are used frequently for paintings exhibited in less-than-ideal environments. In order to minimize adverse effects caused by leakage, often silica gel is added to the packages to buffer the relative humidity. Concern has arisen that the difference between the adsorption properties of silica gel and materials in panel paintings might cause damage during temperature changes. Research at the National Gallery of Art, Washington, studied panel paintings in microclimate packages with silica gel and panel paintings in microclimate packages without silica gel, observing their dimensional behaviour during fluctuations in temperature. Various silica gels were tested. Additionally, panel paintings within microclimate packages were monitored with dataloggers while in shipment and on loan to other institutions. Results indicate that while silica gel is probably not necessary in well-designed and well-constructed packages, adding a moderate quantity of silica gel to microclimate packages used for panel paintings incurs no increased risks and may offer advantages.