An anode bag is nothing more then a filter
The pours in the filter need to be tight enough that they prevent the "fine" particles of the anode slimes passing through the pours of the filter - if the pours are big enough to allow fine particles to pass through the filter they will settle with the fine silver being deposited a your cathode thereby contaminating your fine silver
Even if the pours are tight enough under normal conditions (the anodes &/or anode bag are NOT disturbed) the anode slims can get "forced" through the filter by disturbing the anode(s) &/or anode bag - so "never" play with you anode basket - bag or the anode material (whether bars or shot) after you have set the cell up & started to run it - wait till you are done running it --- do NOT let cathode crystals grow though to your anode bag - they will poke holes in the bag
paper filters don't work because the fibers break down & fall apart when they get wet
So in reality - any filter material could be used as long as -----
1) the pours are tight enough that the "fine" particles of the anode slimes don't pass through
2) wetting doesn't allow the fibers to break down & fall apart
3) is resistant to the acidic condition of the electrolyte
4) is free of other chemical "residue" (examples - bleached material, cloth washed with soapy water, died material)
out side of that - it really is a question of filter material cost - which is why I believe "un-bleached" muslin is suggested as the go to material for anode bag material - its cheap & can be found at any fabric store
I used to buy my (un-bleached) muslin at Joe Ann's Fabric's but the weave was not real tight so had to use at least 2 layers - if not 3 to insure the anode slimes did not pass through--- recently (a couple years ago) Walmart started selling fabric & their muslin is a heavier tighter weave so that only 1 layer is needed
The other advantage to muslin (being a cotton cloth) is it incinerates to a nice "clean" ash when processing the filters - that's due to the creation of "gun cotton" resulting from the nitrates (nitric acid) used to make the silver nitrate
https://en.wikipedia.org/wiki/Nitrocellulose
I am not sure you would get the same effect with other filter material - which "could" mean you "may not" get complete incineration of your filters - meaning possible carbon in the incineration process rather then clean ash
Kurt