How to add face to parallel edges of two hemispheres? I'm making a shallow hemisphere for a 3d printing project. I have to add some "depth" to the hemisphere for the printer to be happy so I made a copy of the current object and shrunk it down a bit. In order to close the shape up I need to add faces to hold these two objects together.

I selected the edges of both hemispheres but when I type "F" it fills each hemisphere independently to itself. I've bool > union these two hemispheres together thinking that would help but it hasn't.

How can I get these two circular shapes to close together making one shape rather than having them close independently making two overlapping shapes?

This is my first 3d project from blender so if there is a better way to be doing this please let me know. Cheers.
Select both edge loops and use the Bridge Edge Loops command.