I have a window a/c unit (~23"w) I install into a small window (30"w) every summer. What are the most efficient materials to use to maximally seal the large & small gaps to keep the hot outdoor air from entering the room? I removed the a/c fins as they do nothing to insulate. I used towels & duct tape in the past but am looking for a better and more efficient solution. Thanks

I have a window a/c unit (~23"w) I install into a small window (30"w) every summer. What are the most efficient materials to use to maximally seal the large & small gaps to keep the hot outdoor air from entering the room? I removed the a/c fins as they do nothing to insulate. I used towels & duct tape in the past but am looking for better and more efficient solutions. Thanks