The construction of the Roll-N-Lock Bed Cover is what sets it apart from the competition. It's not just the superior quality of our vinyl surface material but also the design of the slatted aluminum substrate which supports the vinyl. Each Roll-N-Lock slat is rotatively joined by an interlocking hinge. It is the geometry of this uniquely-contoured hinge that lends Roll-N-Lock its strength, roll compactness and quiet, smooth, non-binding movement. Close examination of the Roll-N-Lock hinge in the flat position reveals the fact that each slat is inseparably locked together, yet when rotated no metal to metal contact takes place.