Pictures and narrative directly from Michael ...
Start with a doubled tube, inside and outside layers flat with hems and slits lined up. Pull the inside tube up and out the top about 6”. The inner hem will be about to the top of the outer slit, as shown in the pictures below:
Fold the top over about 3” or so, making a wide band, as above.
Make another fold, using a little more so it doesn’t bunch and lump.
Now fold the bottom (hem) up to meet the top at the very edge.
Now tuck the part with the hem into the band, getting to the very bottom but not creating lumps, and you’re done.
3 April 2020