I have a 3'x5'x18" outdoor worm bin. When I started it last June I placed an old piece if carpet on top. When feeding I would pull back, feed, add cardboard and recover. Three weeks ago worma began entering the carpet backing, so I removed it. I took 4 food grade coffeebean burlap sacks made of hemp, soaked them awhile and laid them over the top of my very warm bin, creating a 4 layer topper. Now every time I pull back the sacks to feed, I witness a "worm orgy", with several groups of 20 worms or more. They get between the layers of hemp (reminds me of "reefer madness") and now little white worms are abundant as well. The herd seems to love their new enviorment and their appitite is better than ever! ;)