Cut the piece of aluminum to the right size - like 2.5 inches wide. You can have it long and trim later. 23 inches for my 900 ml Ti pot.
Mark lines on the aluminum where you want to fold. 0.5 inch from end for the interlocking closure. Then gap of 2 inches so hot air doesn't flow and heat handle. Then every 0.5 inches. 36 for mine. Then 2 inch gap. then 0.5 inch to where the end is where you can cut it.
Then, just fold over a sharp edged block or table. Flashing folds pretty easy. If you can fold it even just 45 degrees that's enough. Fold back and forth to make accordian.
A "break" would be better if you have access to one. I used one once. Sheet metal working shop.
Drill 4 pairs of holes for the wire to go through.
Then just fold some more by hand to get everything even and properly fit around pot.
Then feed through the wire, bend one end, figure where the other end should be bent and cut off excess.
Actually, just the length of the wire is critical, the flashing can be a little longer or shorter and the width of the accordian folds will be slightly different. You want it to be a tight fit, slightly springing the aluminum against pot, for better thermal contact, and so it doesn't fall off when it gets hot. My previous version did this occasionally.