My coop is mounted inside my garage, with the run mounted on the outside of the garage. The chickens use the open sliding window to go in & out. The run is *very* secure against predators (really, I promise!), so up till now I've just left that window open at all times. As winter approaches, I think that opening will let in too much cold... So I thought about getting a pet door, but the ones designed to fit in a sliding window are way too costly. So I am trying to think of some sort of material I can affix to the opening that would shelter it somewhat, that the chickens could hopefully learn to push their way through. - heavy plastic sheeting? - thick old wool blanket? -????