I purchased 2 of these so my rehabbed and released squirrels could come visit during the day if they wished.  I simply remove the cover, which allows them to come in at their will.  When I leave the room or don't want visitors, I just put the cover back on and they can't open it from outside.  I put a motion activated security camera in the feeder so I get alerted when they're visiting.  The materials seems like polypropylene plastic, nice and durable and easy to clean.  I was actually surprised at the quality once it was all assembled.  It fit in my older wood framed window perfectly and I only needed one strip of the provided weather stripping under my window pane to create a perfect seal.  I have and will recommend this to others.  High marks!