A clip for mechanically securing composite panels, edge-face to edge-face, to supporting structure in the nature of a wall, ceiling, or roof structure having a panel-receiving face comprising a substantially flat surface, said panels each having a rigid board facing backed by a layer of foamed plastic insulating material, said clip comprising a flat web strip having flanges extending substantially perpendicularly from opposite lateral edges thereof, said flanges including a securement flange at and along one edge of the web strip and a pair of flanges extending mutually oppositely at and along the other edge of the web strip, said securement flange being adapted to be rigidly secured, flatwise, to said panelreceiving face of the supporting structure and having its free terminus turned outwardly of the web strip to provide, when so secured, an entry ramp for a receiving pocket defined between the securement flange and the corresponding flange of said pair of flanges.