Why does washing powder leave clothes stiff once they have dried?

The reason may be that detergent residue has remained in the fabric. This may be due to the fact that the washing powder has not completely dissolved in the water or has been overdosed. When you are dosing washing powder, you should follow the information on the pack.
Another reason may be the excessively high degree of water hardness, which is generally characteristic of water in Estonia. In this case, you should add fabric softener every time you do washing. Fabric softeners contain water softening agents, the action of which causes fabric to remain soft.