This combo kit includes 4mm plate foam, 2mm case foam with hotswap cutouts and 2 round 10mm plugs to fill the holes where the feet screw in.
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 CTRL - a keyboard designed and produced by DROP (previously Massdrop).
There are two versions of this combo, the old design and the new design. The old design only works for the CTRL High Profile as that doesn't have any sort of bracing (squiggly lines) underneat the switch plate. If you have a CTRL Low Profile or High Profile with the squiggly bracing underneath the switchplate then you'll need the new version of the design.
If you're unsure if you have a board with or without bracing, get the new design as it will work for all versions.
The diffuser foam may or may not need small alterations.