This paper deals with water vapor transmission properties and thermal conductivity at various temperatures and relative humidities, especially in Nordic climatic conditions. The paper presents measured data for mineral wool, cellulose, flax and sawdust insulation materials, gypsum boards, fiberboards, wood hardboard, oriented strandboard, plywood, wood, weatherization membranes, bitumen paper, and felt and building papers. Effects of increase of vapor permeability as a function of relative humidity, decrease of vapor permeability as a function of temperature, and increase of thermal conductivity as a function of temperature and relative humidity are discussed. In a Nordic climate, a sufficient water vapor resistance of the interior section of building shell and sufficient thermal insulation are required. On the other hand, sheathing must be permeable to water vapor. Changes in material property values can have a considerable effect on the performance of the shell structure.