neil, VM -
FIRST - We're assuming you're talking about dacron, right?
IF so, then:
For some reason both Brownell and BCY are now (all of a sudden) recommending 16 strand dacron strings across the board

. A lot of new (darcon only) bows are comimg with 16 strand strings too

. I don't get it, except for the fact that it's easier to make a one size fits all string - go figure.
The biggest problem you'll have is nock fit. A #25 bow should be using 1716s or there abouts and they take 1/4" nocks - that's going to be tight. There'll also be some speed loss. If you desperately need a string go ahead and use it, but order one from one of the larger distributers or a custom string from one of the guys here like Chad (LBR). "Technically" a #25 bow calls for a 10 strand string, but these days I don't go below 12. I think 12 has a better feel, even on the lighter bows.
IF you're taking about the any of the newer materials:
Seems like they defy the laws of Physics and do use a one size fits all principle

Sorry can't help ya with that, my bows won't let me use anything but dacron
Viper1 out.