For some reason Randy Oliver decided hanging strips would be too labour intensive therefore plumbed for impregnated paper towels placed between boxes in double brood set ups, to me this gives the bees ample opportunity to bypass the towels compared to hanging strips of cardboard right next to the brood nest where the bees are duty bound to try and remove them. A friend of mine who trailed this with inch wide strips of cereal box cardboard found that after a month and a half the bees will have all but nibbled away the strips leaving only the bit hanging on the wooden part of the frame.