Floor panels which are provided with a mechanical locking system including an extruded flexible tongue in a sidewardly open groove which during a vertical folding motion is bent horizontally. A tongue adapted for being received in a sidewardly open groove of a floor panel, wherein the tongue, which is an elongated extruded section, when received in the groove is bendable in a plane substantially parallel with a front face of the floor panel, such that the tongue is at least partially resiliently displaceable inside said sidewardly open groove in said plane during locking of the floor panel with another floor panel and wherein a vertical protrusion, serving as a friction connection between the tongue and the groove, is arranged at an upper or lower part of the tongue, wherein the tongue has a total width that varies in the longitudinal direction of the tongue.