I've been using hard inner covers (Crown Boards) for years, and am now thinking of changing over to soft inner covers (thick plastic sheet, feed sacks etc) - as it's one less bit of woodware to make.
At the moment I'm trialling just the one hive with a plastic sheet - which lies flush on the bars, as that hive is bottom bee-space. It's looking good so far, although I'll be happier when some propolis is attached, as at the moment when the roof is off, the plastic sheet slides around a bit and flaps if there's any breeze unless there are weights on it.
What's the story when using such materials with top bee-space boxes, as there'll then be some 'droop' between box side and top bars ? And, does anyone have any tips or tricks when using such materials ?