Let's talk substrates

[Lija]

well, not sure how in depth you wanna go, I'll just skim the surface as well don't know what frogs are we talking about, but say for a fat frogs:
1. cocofiber:
I don't see any negatives, as long as you change it every month and take out occasional strings before you place a new one in.
positives you listed yourself, it holds humidity well, it doesn't mold, bacterial growth is under control, frog can burrow, that is the most natural substrate for these frogs.
the only negative here is that it is dark colored and frogs tend to blend in, so the colors of a frog will darken as well it is gonna be all dirty ( and happy) all the time. i've never found any sharp particles in there, but you just always have a look and run through your fingers before putting it in just in case.
2. foam filters.
time consuming to clean, you need to do it every day, frogs can't borrow, not natural, but the frogs will be very clean and their colors will be visible very nicely.
3. paper towels.
the most hygienic substrate, is being used for hospital set ups, pros and cons same as foam, but it is better then foam because you don't rinse papertowels thus absolutely no bacteria will transfer from old to a new.
4. rocks, bark, moss.... NO! even if you feed in a separate enclosure it might ingest while shedding.
5. water - these are not aquatic species, no need to keep them like that, back legs atrophy will happen after a few months in that environment and the longer the worse it is gonna be.

all above apply for a fat frogs that burrow. for darts, tree frogs, etc, etc, etc different rules apply. say for waxies cocofiber is not suitable substrate, papertowels or plain felt carpet is a way to go.