As a result of the Industrial Revolution, the sauna evolved to use a metal woodstove, or "kiuas" , with a chimney. Air temperatures averaged around but sometimes exceeded in a traditional Finnish sauna. When the Finns migrated to other areas of the globe they brought their sauna designs and traditions with them. This led to further evolution of the sauna, including the electric sauna stove, which was introduced in 1938 by Metos Ltd in Vaasa. Although the culture of sauna nowadays is more or less related to Finnish culture, the evolution of sauna happened around the same time both in Finland and the Baltic countries sharing the same meaning and importance of sauna in daily life, shared still to this day. The Sauna became very popular especially in Scandinavia and the German-speaking regions of Europe after the Second World War. German soldiers had experienced Finnish saunas during their fight against the Soviet Union on the Soviet-Finnish front of WWII, where they fought on the same side. Saunas were so important to Finnish soldiers that they built saunas not only in mobile tents but even in bunkers. After the war, the German soldiers brought the habit back to Germany and Austria, where it became popular in the second half of the 20th century. The German sauna culture also became popular in neighbouring countries such as Switzerland, Belgium, the Netherlands and Luxembourg.