Best way to make fog?

I’m working on a trench movie and I need fog, what is the best way to get it do you think?

Rob Tuytel has a good way of doing that in this video:

I like it, but does it just annex the built in system?

It uses the Z pass plus some volume pixels.

love it, thanks! I think its even better than the regular mist wouldn’t you say? Any tips for me?

Yes, I think it’s better than regular mist. Bartek also has a way to make mist, a bit more complicated, but good results: