The square-shaped grow lids offer 5.5mil thickness, and its diameter is 8’’. The lids come in dual colors, which are black and white, and each has a purpose. The white-colored lid helps to reflect light towards the plants, whereas the black lid helps keep algae and mildew away while also ensuring that pests do not attack the plants. The lids are available in square and round styles. Both the lids are available in a pack of 40.