I've tried wooden, plastic, and masonite inner covers and I don't care for any of them. The inner cover provides a haven for ants and the extra activity in removing the cover provides an aggravation both to the bees and the beekeeper. Unless I find something cheaper, I use plywood (I really like BB formboard grade), tack and glue about one-half inch of regular wood on each edge and use cleats on the ends. I also cover mine with offset plates from the print shop. What I have told you also identifies myself as a part-time small operator, retired and not concerned about the extra time. I am aware that large operators would not do it this way. Jim Shoemaker 5160 S. Western Brookline, MO 65619