I liked the idea of the channels to slip in a paper label, but I could never print that properly. So this flag is a solid 26 x 33 to perfectly accommodate a 24 mm x 31 mm adhesive label sporting information about the filament or a QR code to an information site.

Note that the flag blocks access to the back window, so if you're hanging your Benchys (?) with a hook through that opening, this may not work for you.