This combo kit includes 4mm plate foam and 2mm case foam with hotswap cutouts.
Installation requires taking the board apart, putting the plate foam inside, slipping the PCB back into place GENTLY, putting the case foam on the PCB, putting the 'acrylic' (plastic) diffuser back into place, press all of the plastic plugs in tightly to hold everything together and then screw the top half to the bottom half.
These foams are designed to fit the ALT LOW PROFILE - a keyboard designed and produced by DROP (previously Massdrop).
Small note: Drop has recently added a brace to the ALT. To account for this divider there is a scored a line in the foam for you to cut along if your ALT happens to have this divider.
Even smaller note: Works for both High Profile and Low Profile variants.