Yard Guard HPI-R5X5-1836GBM99 18' x 36' Gray Rectangular Bloc Mesh 99 - The Yard Guard Deck-Lock System is the latest in pool cover technology. It comes in either high quality mesh or reinforced vinyl and reinforced webbing both top and bottom on every seam protected by rub strips. Block Mesh 99 has a tighter weave and provides 99% sun blockage, which is ideal for reducing algae and sediment build-up. If you want the best for your pool, Deck-Lock Bloc Mesh 99 is it.