making covers for fan, door window and shower skylight

We found that a kitchen chair foam pad fits just tight enough to stay in place.
When we have hot weather to contend with we use a square of the bubble type foil along with the foam pad.
It cuts the light and works as a pretty good insulator
For the door window,we use a couple of velcro strips near the top of the window
to hold another piece of bubble foil.