Crushed panne velour(poly) is super stretchy and makes a great wicking inner layer. It is a pitb to sew, but using lots of pins and spraying with spray starch helps immensely.
Plus if you go there, at least my store(I'm in ND) has cotton swimsuit elastic, which works a lot better for diapers than the stuff you buy at Joann's. I need to go get some more actually.
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