I think a lot of people regard Washi stocks as 'artistic' film - unpredictable, gimmicky, not to be taken entirely seriously. While this is perhaps true for some Washi formulas, for me 'F' is the major exception and perhaps my favourite black and white stock.
Repurposed from film designed for chest x-rays, 'F' has a velvety soft contrast falloff - gentle points of black graduated all the way to milky, grainy white. There's a lovely soft highlight bloom as well - no need to pack a promist filter, 'F' has the look straight out of the can.
Even in high-contrast environments (see photo 2), detail is retained well and the grain really shines. The grain itself is big, crunchy, and oh-so characterful. Paired with a sharp lens, 'F' renders landscapes gorgeously. (I'm yet to shoot any portraits with it, so can't speak for its abilities there.)
'F' is definitely a little trickier than some stocks - it is prone to leaking, light piping, and vignetting - but returns much more reliable and consistent results than other Washi stocks I have tried.
The gentle, ethereal glow is a look I've tried to emulate with many other BW stocks - 'F' achieves it with such ease, and is a complete winner in my book.