Wood logs are considered the best material for the construction of the Finnish sauna. Birch, aspen or linden. Natural wood has optimal heat resistance and moisture permeability. Do not cover the internal walls with paint and varnishes, t. To. They reduce the absorption of wood with moisture and jaws from the effects of high temperature. By the way, after the construction of the sauna, it will not be superfluous to change the castle at home, useful information then see here MOS24.SU.