Hi, I would like to make a mold in Zbrush of a face I modeled and use that to be filled up in Realflow, to create a face filling up with water. Does ZBrush have default mold or an easy way to do this as I have seen something similar on other peoples ZBrush work. Any help would be great, thanks 
You have some options. Sculpt the face as you normally would.
If you’re using only ZBrush, and you made the back of head, hide it leaving only the face visible. Geometry pallet>Delete Hidden to delete the back of the head. Go down to the Display pallet, make sure double sided is turned of, then hit Flip to flip the normals. Now you can use it as a collision object for your particle system.
Alternativley, once the back of the head is hidden, set the thickness slider as desired in the SubTool pallet, then hit Extract. This will give you a new subtool “shell” of the face.
The second method gives you thickness, the first doesn’t. Thickness isn’t necessary for a collision object, and it may even increase your simulation time.
db