To provide a comfortable wall structure in which dew condensation in a wall in winter and summer is prevented.

A heat-insulating material 1 used in the wall of a building has properties in which thermal conductivity is 0.07 W/m.K or less, moisture capacity as the difference of relative humidity of 80% and moisture content of 50% is 1.0 vol% or more and permeability is 2 ng/m.s.Pa or more. Accordingly, when the heat-insulating material 1 having high humidity capacity and high permeability is used, moisture in the wall is absorbed and held into the heat- insulating material in a short time, and discharged to an interior substrate material 2 and an exterior substrate material 3 for a long time. Consequently, the generation of dew condensation on the surface of the exterior substrate material 3 cooled by the outside air in winter and the surface of the interior substrate material 2 cooled by cooling in summer is prevented.