The Dual-sided 5.5mil grow lids are available in round and square styles. They have a white face to reflect light back to the plants as well as a black side to block light and help with algae, mildew, and pest control. The Dual-sided 5.5mil grow lids are available in round and square styles. They have a white face to reflect light back to the plants as well as a black side to block light and help with algae, mildew, and pest control. Sold in packs of 40.