Without any foam, the sound from the planck is inconsistent. Keys just a few keys apart sound very different. I originally had some case foam I cut from a sheet of packing foam for dishes, and it helped, but with this kit, the sound very consistent. The sound is a bit more muted (I mean that in a positive way), and all the keys sound roughly the same.
Aluminum can ring at times you don't want it to, so this bit of foam was the precise needed for my Planck to keep it calm. Great quality and all you need.
im running the ttc silent frozens with switch stickers, and the foam pad on the tpu planck. hands down the quietest board i've ever used and I find myself grabbing it on the daily now nice I've become accustomed to the layers and ortho layout.
The foam adds a better bottom out feel and killed the last bit of ping the board produced. 10/10 fit and function without impacting the led brightness.