Question: I would like to turn two regular spaced grids (so same amount of vertices, spaced at regular intervals) into a volume in which the top plane becomes the top of the volume and the bottom plane the bottom of the volume. 

[![top and bottom plane](https://i.stack.imgur.com/joKlo.jpg)](https://i.stack.imgur.com/joKlo.jpg)

I've succesfully done this duplicating the two planes (save for later), then join the original two planes and then in edit-mode -> "Bridge faces". This would remove both planes and leave me with he outer band of the volume (see image)

[![outerband of the volume after bridging the faces of the planes](https://i.stack.imgur.com/mCyjy.jpg)](https://i.stack.imgur.com/mCyjy.jpg)

I then placed the outer band between the previously duplicated planes. Job done.

[![Outerband with the original planes ](https://i.stack.imgur.com/sTiJT.jpg)](https://i.stack.imgur.com/sTiJT.jpg)

But this is a bit of a pain in the neck because i would like to do this for a lot of sets of planes. And also do this with irregular spaced planes and regular spaced planes with a different extend.

Is there a method or workaround to do this more easily?

[![](https://blend-exchange.giantcowfilms.com/embedImage.png?bid=g51dplek)](https://blend-exchange.giantcowfilms.com/b/g51dplek/)

Answer: 
*Bridge Edge Loops* should work here. 

1. Join both planes into one object through *Object > Join*, `Ctrl+J`
2. Use *edge* selection and go *Select > All by Trait > Non Manifold* (to select the loops)
3. Then *Edge > Bridge Edge Loops*

[![enter image description here](https://i.stack.imgur.com/t0PJ8.gif)](https://i.stack.imgur.com/t0PJ8.gif)

*Edit:*  

In your case, the mesh has two forgotten edges in one of it's corners (one on each plane). Just delete them an it will work no problem.
After all that you can [recalculate normals](https://blender.stackexchange.com/a/165081/78972) so they're all pointing the right way

[![enter image description here](https://i.stack.imgur.com/fUZgO.gif)](https://i.stack.imgur.com/fUZgO.gif)
First you need to make the two elements a single object. **No vertices can belong to two different objects**.

Using bridge edge loops doesn't work because of two sets of vertices on two different corners. Bridge edge loops works only with closed loops.

There is a lonely vertex with no faces that cannot be part of a closed loop

[![enter image description here](https://i.stack.imgur.com/Z2uBP.png)](https://i.stack.imgur.com/Z2uBP.png) 

Then, there is a single quad on some other corner. Technically that quad in itself is a closed loop, so if you use bridge edge loops that is the only loop that will get new faces.

[![enter image description here](https://i.stack.imgur.com/3XUc7.png)](https://i.stack.imgur.com/3XUc7.png)

So you can simply ignore those (or delete them) as part of the selection at the edge and use bridge edge loops successfully.

[![enter image description here](https://i.stack.imgur.com/gJKJB.jpg)](https://i.stack.imgur.com/gJKJB.jpg) 

If you still need faces for the elements on the corners, add faces manually.

---

Now as a comment of workflow used in the original question, it is still valid, but will result in duplicated edges and disconnected geometry so it is not "job done" but "almost done" to finish the job you need to use "merge vertices by distance". All vertices should be then connected as part of the same object.