Review (3/5): Cute, but not as adjustable as I'd have hoped
This material seems quite waterproof without a shiny plastic coating on it, which results in a softer, quieter shower cap. So I'd say it's a really nice shower cap if it fits you as is!
However, for adjustability you can untie the bow to tighten it up if necessary, but you end up with a gaping crease behind the bow (and unless you're more talented than myself- a bow that doesn't stay aligned, and looks much worse than the one it came with). I tried to swing that gaping opening and bow to the back of the cap for a shower, but of course it still let water in underneath it.
If you anticipate having to tighten this as I did (skull diameter measuring at 22" around where the cap sits), I would look elsewhere.