Coffee can filters are the dangerous kind. There's no way to be 100% sure but if it's a coffee can, I wouldn't breathe through it, ever, but if you want to try: shake the filter. Do you hear a shaking sound? Like maracas? If you do: filter is damaged, don't use it.
If you don't, if you hear NOTHING AT ALL, then try banging it with a bit of force, uncapped, against a white piece of paper to see if there's shit coming loose through the breathing side.
If there isn't, then you can try it on, it might be safeish.