Wash and thoroughly dry the aluminum can.
Place the can on cardboard and trace around it. Cut a round piece slightly smaller than the tracing so it fits snugly in the bottom of the can.
Place the round cutout inside the can. Measure the height from this insert to the top of the can.
Transfer this height to corrugated cardboard and cut it to size.
Roll the cardboard to fit comfortably inside the can, leaving a little room for adjustment. Position the cut side down, as it will compress from cutting.
Slide your files into the cardboard corrugations to keep them separated and protected from knocking against each other.
To easily identify the files, color code them by wrapping pieces of colored tape around the handles, as well as write on pieces of the corresponding tape affixed to the outside of the can.