[pehtis]

Its called soft touch or "rubber oil". It's basically silicone suspended in plastic which gives that soft touch feeling before it biodegrades to the sticky goo.. We can easily clean that with isopropyl alcohol. You will be left with the clean hard plastic below that layer.

[kevin_thibedeau]

There are two variants: One with the soft touch sprayed on after molding, the other mixed in with the pellets before molding. You can't do much for the latter.