The popper WNOS we had were a great fit on Iris, until the day that two new ones arrived. Then they started to fit horribly, regardless of what I stuffed them with. She'd just changed shape and we couldn't get a good fit. So I sold them on and bought some touchtape WNOS; they fit really well. And, of course, she's now changed shape again and the one popper OS I'd hung onto also fits.