We used insulation board from Lowes or Home Depot with foil on one side and foam pipe insulation. Cut out the board to fit minus the foam pipe insulation thickness. Cut the foam pipe insulation to fit the entire perimeter. Glue the pipe insulation onto the board. When you finish you should have a board with a round bumper all the way around the board. When finished press it into place in the skylight. Cuts out the light and insulates too. It installs and removes with ease.
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