The TNF sleeping bag I was planning on using for a trip is tight in the shoulders, so I was going to buy a TNF Expander, but none of the places I tried had any, and I looked at a LOT. Apparently, TNF had made them for a few years, but then stopped, or at least outfitters didn’t have them. I have since found a place that got some in, but I’d already made my own. I also looked at a Big Agnes item that is similar, I think they call it a wedgie, and the only ones I found were the wrong type of zipper. So I decided to make one. I got some leftover fill, from my Kennebec project (which turned out really nice, by the way) and some old rip-stop nylon, and a YKK #8 zipper, and I made one. It worked fine. I used it on a three week Yukon/Alaska canoe trip this summer, and had a luxurious amount of room, and was pleasantly warm. Thanks for asking.
Beth