Wood is an excellent, renewable, CO₂ neutral building material, which if properly used, protected and installed, boasts a particuarly long lifespan. Various methods of modifying wood to improve its resistance without the use of chemical treatments have been developed over the past two decades; one such innovative development is thermal modification.

Thermal modification is one of the newest methods to protect wood against fungi and insects. Thermal modification dramatically increases wood’s durability without the use of chemical preservatives. This in turn extends the lifespan of wooden windows considerably. These windows also take on an exotic look due to the darker colour that results from thermal modifification. The natural resistance of poor resistance species (e.g. spruce - resistance class 4) increases enough to produce a resistance class 2 species (European standard SIST EN 350-2) with thermal modification, which means that thermally modified spruce has a resistance comparable to the far more robust oak and chestnut. Thermally modified spruce can therefore be substituted for Siberian larch or meranti, which are commonly used for use in windows because of their higher natural resistance.

Windows from thermally modified wood can also be produced and used without a surface treatment (coating), in which case the wood naturally develops a silver colour after some time. Alongside longer lifespans, these windows are also more dimensionally stable, as thermally modified wood swells and shrinks up to 50% less and absorbs less moisture from the air. Thermally modified wood also demonstrates better thermal characteristics, exhibiting lower thermal conductivity (?) than unmodified wood. Thermal transmittance of window frames (U_f) made from thermally modified spruce is significantly lower, delivering roughly 20% better insulation values compared to U_f made of normal spruce.

Spruce also played a central role in the development of the M SORA Natura Optimo XLT passive window, which won first prize at the German Institute for Passive Buildings (Passivhaus Institut) taking home the Component Award 2014. This window is made ??of spruce that is thermally modified using a unique, high-tech process of thermal modification called Silvapro® Wood, and is the result of extensive Slovenian research and development. The process is carried out by the Slovenian company Silvaprodukt, with whom M SORA works in collaboration in both research and in the organization of various related public events.

M SORA is well equipped to produce all types of windows from thermally modified spruce in a variety of styles and colours.