The Crazy Outdoor Mama
Tape your see through paper over your window. Trace the contours of the window. Remember, this is to be placed INSIDE the frame, so trace the inside, not the outside!
Remove see through paper and tape it to your foam board. Start cutting out the window shape with an exacto knife. Leave a small notch so that it's easy removable!
Once cut, make sure it fits by testing it in your window. It's good to fit snug! Bring it in the house to prepare to glue the material to the foam board.