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No, I meant the same material used for making windshield sunscreens and insulating under the carpet. It's been more than a while since I did mine, and at the time we had a local Orchard Hardware that carried the very reflective material on a roll. I bought two or three feet -- I'd have to check my pattern for how much I needed.
For generating a pattern, I used several sheets of printer paper on the inverted top. Placed a sheet of paper close to or under the frame edge, then marked it with a Sharpie. Trimmed until if fit along the paper's full edge. Added a sheet for the next section, then taped the sheets together. Bing, bang, boom, and I had a pattern of the inside perimeter of my top frame.