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Using numerical simulation tools, we calculated the temporal evolution of heat and moisture transport in train walls including condensation and evaporation processes. The calculations are based on data (temperature, humidity, etc,] that were measured on an operating train during one year in Switzerland. The calculations were carried out in one dimension with a characteristic wall structure that allows unhindered moisture exchange between the train interior and the thermal insulation. Despite the moisture exchange, the calculations show no longterm accumulation of moisture in the insulation. On the cold side of the insulation, the water content may increase depending on the temperature gradient and interior humidity, but the insulation dries up again within hours to a few days. During times of high water content, the increase of the water content is only significant within a few millimeters on the cold side of the insulation. Therefore, the thermal conductivity of most of the insulation remains low and the insulation maintains its insulating function. [ABSTRACT FROM AUTHOR]