Filter paper is graded by qualitative/quantitative; speed (or pore size); thickness; binder or no binder; low ash or ashless; and hardness. Other manufacturers of filter papers such a Ahlstrom have charts which show equivalents between their papers and other brands.
Pall Life sciences has alternatives to Whatman’s capsule filters and membranes. Corning has alternatives to Whatman’s bottletop filters. There are alternatives and now would be a good time to verify the use of some of the alternatives in standard procedures. For help in choosing suitable alternatives consult your laboratory supplier.