Edit: Couldn't edit my previous post, so I'm not confused:
There are also "rougher" keycaps other than PBT, compared to the smoother ABS, even if PBT are "rudely light". I don't know if this is the kind of keycaps you were talking about, they are called: Rubber, very recognizable compared to the other types of keycaps. Digitec sells some from Ducky here ->
Ducky Rubber Keycap Set, 31 Tasten
In short, practical I think on some keys (W, A, S, D or F+J for tabulation, etc) but never tested, so I can't say for sure ^^'