When good thermal insulation is needed, double log is right choice for wall material. In this kind of construction there is a space between two logs, which can be filled with wood fibre insulation. When k-value for 202 mm thick log wall is 0,53 it is improved to 0,17 with insulated double log (90mm log + 175mm insulation + 90mm logwall. (k-value is used to descripe capacity of thermal insulation).