Optimum covers are vinyl covers with beading attached to them. This is designed so it can be combined with a double sided receiver. In this case, the receiver goes on the pool wall under the top rail. The beaded cover gets inserted into the track that is on the outside of the pool under the rail, then the cover goes over the pool like a drum cover. These can also be made with an inside receiver that would be located on the inside of the pool above the liner receiver.