I was close to buying a wellie warmer from L L Bean when I saw this tutorial. I went to the fabric store to buy the materials, which cost me less than $5! I'm now working on the cuff fold for the first pair. I hope it works!
Update:
I am done with the first pair. It's taking me longer to finish the warmers because I can only work on them on week-ends (and not every week-end for that matter). I am also sewing them by hand. Here are photos of my wellie without and with the warmer.
