I think it is piano wire (also known as harp wire) with a couple of ground level hotwires which you can see if you look very carefully unless I'm mistaken. I believe the Bronx Zoo has the same kind of barrier for its snow leopard enclosure.
As does much of the rest of the exhibit, although IMO Zurich did it even better. The lack of a mesh roof makes this an even more impressive exhibit, but they "lifted" many of the public area/viewing structure details lock stock and barrel from Himalayan Highlands!
I visited Zurich Zoo in the fall of 2003 (one of 2 European zoos that I've been to!) and the snow leopard exhibit there is the best that I've ever seen. Himalayan Highlands in the Bronx is also excellent, but in terms of size and scope the Zurich habitat is outstanding.
I am convinced that harp wire is the best barrier solution for close viewing. Windows have become common practice for too many zoos and its just never the same, you dont hear the same, you dont smell the same, there is glare and distortion, there is much more of a disconnect between you and the animal like your watching it on a screen. Harp wire is the easiest for our eyes to look past so I find.
