Short answer: Yes.

Alright, thanks for reading, everybody!

Just kidding.

Long answer:

Generally, foam will deaden reverberation – so you’ll still hear the clickies click obviously, but they won’t resonate through the case as much. How much a difference it makes will depend on a few things, mostly how much empty space there is and what material(s) the walls of that space are made of. Another big factor is the roof; the plate and PCB – how flexible those are and what they’re made of.

If there’s lot’s of space and the walls are something like rigid aluminum, you will notice a pretty big difference no matter what dampening you use, and will probably notice the most difference between types of dampening. If it’s a really small space with mostly plastic walls, you can definitely still tune it but the changes won’t be as drastic.

Generally, the more flexible the plate-and-pcb assembly, the deeper of a sound it’s going to send down into the chamber below. Inversely true with more rigid assemblies; those tend to be more high pitched and sharp. Both and the spectrum between will change with dampening, but not necessarily in the same ways. The more flexible assemblies will also tend to be louder and reverberate more, but by the same token you can put a sock in that both by absorbing the sound waves with dampening material and/or by dampening the assembly’s vibrations through direct contact. (Just make sure to be gentle; don’t force anything and you should be good.)

From there, you can tune the degree and character of dampening with density / composition of foam.

Polyfill (stuffed-animal / pillow stuffing) can do wonders to clean-up a harsh chamber without totally silencing it, and because it’s fluffy and compressible (and cheap) you get a lot of range to dial-in your preference. At the other end, something like Sorbothane is super dense (and expensive) and will pretty much stop sound-waves in their tracks. It comes in a variety of thicknesses usually in the form of sheets. The thin foam that tends to come with electronics like keyboards is legit useful for sound tuning, either between the plate and PCB or below the PCB, and that stuff is basically free.

Some keebs have silicone wedges that fit in (like the KBD67 Lite, Portico, and a bunch more), or you can pour it in. I’d do some research if you want to try the latter; it’s not too hard but you don’t want to approach it blind. That stuff is heavy, dense, and pretty firm – it actually does make the typing feel more firm if it’s close enough to the PCB to reduce (or negate) its range of flex.

If you want a more solid-feeling typing experience and some sound deadening without changing any other bits, this might be the option. For clickies I think this would be fine for the sound, same for silents – but for thock-chasers et-al I’d be more hesitant in recommending filling-up a chamber with something dense like that.

If you think you might want to give that a try, I found a video guide by Mandydeth on YouTube about doing a silicone pour for a Preonic / Planck. He doesn’t have a recording before for comparison, but he is using clickies in his sound test, and there’s also some good pointers and discussion in the comments.

Alright, that’s my primer on case fillers. Thanks for coming to my TED talk.