The temperature and relative humidity inside packing cases during the transportation of works of art have been monitored using solid-state data loggers. The relative humidity has been found to be quite stable, regardless of changes in temperature which occur as the case equilibrates with external conditions. The thermal half-times calculated for a number of cases agree with those reported previously. The way in which the environmental stability is affected by the composition of the artifact and by variations in pressure during takeoff and landing is explored.