Thanks Zber2 and Doug.
The model in question is a bit of a tricky one to hide or mask the bits I don’t want - hence the question about whether I can just mask visible faces which would be the ideal solution to my particular issue.
My model is like this…

I want to mask just the back bit…

And not mask the other side like this…

I am sure that I can hide/mask to get the job done with some fiddling, but I thought I’d ask if there was an easy way! I am finding that Zb is one of those apps that if I hunt for a solution (or ask in this case!) there is always is a way!!
(A case in point - I just discovered I can do screengrabs in Zb!!)
Thanks again for your thoughts
Steve