Last Summer I attended the international calligraphy conference "A Show of Hands" in North Carolina, where I was privileged to learn more about making and using a folded pen from Carol DuBosch. She had envisioned and then created a "pen burrito" filled with her collection of folded pens. I immediately knew I needed one too! In case anyone else is interested, she graciously gave permission for me to share the simple process.
I started out without referring to my notes, so I bought more plastic than I needed. The Joann's where I purchased it had 50" width so I only needed 20" and that would make two if you make them 25" wide (25 pockets). You want it to be a medium weight - not thin but not too stiff.
Here's what mine looked like. If you want about 30 pockets, use a piece 30" by 20", folding the long edge up a little over 4" as shown. I used masking tape to hold things in place. That leaves over 15" which gives you a nice generous flap to fold down over your pens.
To make it easy to sew pockets fairly even and straight, I used more tape to mark them. I slid the yardstick underneath and put a piece as straight and evenly as I could midway between every other inch. That way I could sew along the edge on both sides for pockets about 1". You could make them bigger if you want to stuff in multiples or fat pens.
That's really all there is to it. trim threads, slide in pens (they might be a bit fussy to get in the first time, as the plastic likes to stick to itself but it will get used to the new shape), fold down the top flap, roll it up! Your pens travel safely, are easy to see and select. You could adjust to any size - if you make one too big, just take scissors to it.
I'm really looking forward to Carol teaching at LetterWorks next summer in Utah! Hope to see you there.