PLASTIC TOP FOR TRAY ( 1020 FLAT) 7" high, clear top for above trays used to retain moisture. Extra Heavy Duty!THE PICTURE MAY VARY SLIGHTLY TO THE ACTUAL PRODUCT. You may want to cut holes in the top of this dome to let air escape. Likewise, you may want to cut some small holes along the base where it meets the bottom tray. This will allow air to travel in the small holes and up through the ones in the top. This is called convection venting and will allow for a small but steady flow of air through the cuttings or seedlings and will help eliminate mold and mildew without drying the plant leaves. This procedure is mandatory when using a heat mat. I can hear you thinking. Where do you cut the holes? The dome’s top has to two flat squares that can be cut out and the at the bottom there are six dimpled squares that can be cut out.