The increased demand for space led to the relocation of operations to Sonneberg (Thuringia) in 1934. During this period, plastic parts were used for the first time. Thanks to their outstanding insulating properties, they were soon increasingly manufactured and used by Kopp. Before the war, the company exported up to 85 percent of its products, mainly overseas.
Despite the difficult conditions during the war, the company managed to defend its position and even to expand, with up to 500 employees bearing testimony to this. At the end of the war and during the expropriation without compensation in the Soviet-occupied zone, the fate of the company appeared to have been sealed. However, entrepreneurial activity then led to a rebuilding in Kleinblankenbach in Kahlgrund.
