We have used these insulated hive tops on our hives for the last few years with good results. The M-V insulated top consists of 3 ½” deep rim with screened ventilation holes around the perimeter which allow water vapor to wick away. The holes are inclined upward to prevent rain and snow intrusion. The top and bottom of the rim are covered with 1/8” hardware cloth (with the appropriate bee space on the bottom). Sandwiched between the top and bottom layers of hardware cloth is approximately 3 ¼ inches of cellulose insulation. The bottom screen is lined on the inside with cotton fabric to prevent the bees from picking at the cellulose insulation. The lower rim is notched to provide an upper winter entrance for your bees. This unit is used in place of your inner cover over the winter.