This mutation is found in Maas Neotek. Once you get there, head to CL on the map, entering the building from the west side (going east to enter it). You'll need to run past some nasty hepcats, or fight them, to get to the mutation. The hepcats you need to kill on the way up are fairly easy, and only use switchblades to fight with.
This mutation grants:
+3-6 electric +1-3 acid resistance
Takes up a soak slot.
He/She has tough, rubbery skin.