I used that rigid insulation from Lowes or Home Depot too...covered it with flannel. The pieces stick without pinning...or you can put pins in it...either way it works well and is very inexpensive. I like the idea of being able to roll it up like the window shade. I wonder if you can put flannel on a window shade and roll it up? If anyone tries this, please let us know. BTW...the bigger the better.