The pillar is fiberglass too, I believe.

There's a (mostly terrible) documentary about a previous bansky "statue" deposited in London that, in one of its better moments, tracks down the people who actually make statues for artists like banksy.

https://en.wikipedia.org/wiki/The_Banksy_Job

edit: I feel I should clarify that this is not an official Banksy documentary. He made "Exit Through the Gift Shop" which is an amazing film which I highly recommend to anyone.

Aw, it's Fiberglas? Not bronze and stone?

The Wall Street Bull was a guerilla art piece too. It's a real bronze. Weighs about three metric tons. It's hugely popular, although it's been moved a few times. Banksy's work should be replicated in bronze and stone and placed permanently.