Established in Helsinki in 1914, the brush factory was one of SOK's first factories. In 1917, the factory was moved to Vaajakoski, where SOK had no other production plants at the time. The new brush factory began coperation in Varassaari in Vaajakoski in 1937. During its peak years in the 1930s, the factory manufactured almost 300,000 brushes of various types annually, along with 150,000 paintbrushes.

In the 1920s–1940s, cooperative activities in S Group became a central force in economic life and an influential factor in the Finnish society as a whole.

By its purchase power, SOK was the leading Finnish wholesale dealer, in addition to which SOK founded a significant amount of industry of its own, securing the availability and quality of goods sold in cooperatives. As early as in 1919, SOK had founded a match factory in Vaajakoski, near the city of Jyväskylä. In 1920, SOK took into use a 0.5 megawatt hydropower plant and a paper converting mill in Vaajakoski. Furthermore, itbegan to process berries and manufacture sweets in a berry factory.In 1921, a sawmill and a wood processing mill were set inoperation in Varassaari.A margarine factory was completed in 1928,and a sweet factory in 1929.Brush and nail factories started their operations towards the end of the 1930s.  

Business ideas were developed,and the service network was reinforced in all lines of business. The sprouts for a business chain were already planted in those days. New members were acquired and the consolidation of customer relationships was highly valued.In fact, S Group was already a pioneer in the customer loyalty concept in Finland.

Right from the beginning, the training of cooperative employees has been a significant element in the activities of S Group.SOK's cooperative school was set in operation in October 1919.In the summer of 1950, the first courses were held in Jollas in Helsinki.

Wartime

During the wars and the rationing period that followed, SOK, together with other central trade corporations, participated in the work of various financial committees set up by the government.

In October 1939, on the verge of the Winter War, SOK handed over bicycles as well as the entire stored production of its margarine factory in Vaajakoski to the Finnish Defence Forces.The Defence Forces also took over the flour mills in Vyborg and Oulu, the nail factory in Vaajakoski, which manufactured barbwire, as well as the textile factory and knittery in Helsinki.