Mechanical locking system for panels and method of installing same

A set of floor panels which are mechanically connectable to each other along one pair of adjacent edges, each of said floor panels comprising:

• one or more upper layers of a decorative plastic material, and an intermediate core of a plastic material;
• a flexible tongue on a first edge of the panel;
• a tongue groove on a second edge of the panel for receiving the flexible tongue of an adjacent panel for mechanically locking together said adjacent edges at right angles to a principal plane of the panels thereby forming a vertical mechanical connection between the panels, wherein the tongue groove is formed in a core of the panel;
• and
• a locking element formed in one piece with the panel at the first or the second edge and a locking groove at the other of the first or the second edge, the locking groove being open towards a rear side of the panel that faces a subfloor;
• wherein the locking element and the locking groove form a horizontal mechanical connection for locking the panels to each other horizontally parallel to the principal plane and at right angles to the joined first and second edges,
• wherein the flexible tongue is resilient and formed of a separate material than the core, and cooperates with the tongue groove,
• wherein two of the panels can be mechanically joined together by displacement of said two panels vertically towards each other while at least a part of the flexible tongue is resiliently displaced horizontally until said adjacent edges of the two panels are brought into engagement with each other vertically and the tongue is then displaced towards its initial position against the tongue groove,
• wherein the flexible tongue has an inner part mounted in a sideward open groove, in the first or the second edge, and a protruding part, wherein the inner part is fixed in the sideward open groove, and wherein the part of the tongue which is resiliently displaced is the protruding part.