According to the official website for the Chemex products, the filters available for the Chemex are:
- CHEMEX BONDED FILTERS PRE-FOLDED CIRCLES (FC-100)
- CHEMEX BONDED FILTERS PRE-FOLDED SQUARES (FS-100)
- CHEMEX BONDED FILTERS PRE-FOLDED SQUARES (NATURAL) (FSU-100)
- CHEMEX BONDED FILTERS UNFOLDED HALF MOON (FP-2)
The 10 cups Chemexes, are:
- TEN CUP GLASS HANDLE CHEMEX (CM-10GH)
- TEN CUP CLASSIC CHEMEX (CM-10A)
which both uses the same filters:
Use CHEMEX Bonded Filters FP-1, FC-100, FS-100, FSU-100
The dimensions for both Chemex are the same (at least, height and diameter), so the shape should be the same. My opinion is that it's just an illusion that feels like the filters fit in a different way. Maybe you can put a filter both side to side and compare them :P
I prefer the FS-100 (the square corners comes very handy when removing the filter), but given that all filters have the same size (when it comes to filtering area), all of them should behave equally (except the natural vs bleached).