Metal, never nylon (shiver me timbers). Black nylon I've never seen. I wonder what they sound like now. I'm sure there must be improvements from what I am familiar with. A combo....that's even more interesting. What brand did you buy?
LOLOL, changing the strings (surprised I remembered how)...I did it last night, snapped the low E (never done that before), put on another, tuned it up and got lost in it. Was a pretty special experience in several ways, lots of memories. I've snapped more high E & B strings than I care to count and my thought is always, save the eyeballs, no wire contact with eyes.