I just made some serged edge knit cotton terry flats. Pros: they are very soft and absorbent, cons: they are thicker than Birdseye, alot thicker. I only padfold my flats so I can't say wether a snappi works well or not. I will be making some flannel flats to try out next. I don't think that quilting cotton would work well as it is not very absorbent. I bet your thermal knit would work well though.
Rachel, SAHM to
wife to dh .