Having recently taken delivery of Vax S2 Hard Floor Master Upright Steam Stick
which I'm delighted by, I thought I'd check out whether Amazon sold the replacement heads for that model (no) Though sold by Vax (though currently showing out of stock) they seemed expensive, so I began to trawl through other models with a similarly shaped head. Took a chance on this very thick, clearly highly water absorbent model for the H20 mop, as sold by Zary. Bingo, it fits the Vax beautifully (and, according to another reviewer the H20 mop heads also fit the Bionair) - I guess a fairly universal triangular design compatibility! This thicker mop head is great - robust highly water absorbent, making for a more instantly dry floor. The only downside would be you will find more resistance in use than with the other completely flat, unfringed heads, so this requires a little more arm strength in mopping. Nothing major, but if someone was very frail, the flat heads are easier, though leaving the floor a little wetter.
Oh, and though this is a 5 star review of the product itself, the supplier (Zary) deserves 5 stars as well.