You mean In regards to Feels Kafka? =)
Not sure if I can describe it very well, but I use a gon crystal 60 with lubed gateron blacks daily which is a fully carbonate case and plate.
The fully pc setup definitely makes the board super quite and gives it very unique smooth feel compared to a hard pingy metal feel.
It doesn't feel noticeably soft but definitely a lot less harsh then steel or even aluminum.
It's hard to describe honestly as it doesn't feel plasticy at all.
Maybe search for lastpilots crystal tkl buildlog and look at his typing vid, it probably pictures sound and feel better then I could describe it XD