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I'm a complete novice at Blender 2.8x, and I'm trying to create an object whose surface is defined by a deformed plane. Basically, I'm trying to recreate this effect. When I try to perform the boolean, however, it seems to only sometimes work depending on the position and rotation of the plane. An example of the broken effect, where both sides of the object disappear: Broken boolean effect

While at a slightly different rotation it works as expected: enter image description here

I know that the boolean modifier works best with manifold objects, but I've seen several sources online that say you can use the boolean modifier in this way. Is it simply undefined behavior to use it with planes instead of another manifold object?

I also found many posts online whose problems were caused by coincident vertices or messed up normals. But I don't see how this could be the problem since the issue is replicated with a simple default cube and a plane.

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Since Blender 2.91, you can boolean with manifold objects like a Plane.
There are two methods now. The Exact method should solve your issue.

old 2.9x Fast (2.8 method) enter image description here

new 2.9x Exact enter image description here

It is cut out in inside normal direction (red color when Face Orientation overlay enabled).

enter image description here

If you still need to work in 2.8 you would have to use Solidify modifier or other tech to create non-manifold object as you mentioned.

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    $\begingroup$ Thanks for the info! I've been trying to avoid using 2.9 since I've found a lot more tutorials for 2.8x, and I figured it would have less bugs than the newest version. But, looks like learning the new interface won't be too bad, since it seems to be fairly similar to 2.8. $\endgroup$
    – David_32
    Commented Nov 9, 2020 at 20:02
  • $\begingroup$ How do you get it to remove the part inside the normal direction? I can get it to cut through the object but both parts remain. $\endgroup$
    – Bas
    Commented Apr 3 at 7:10
  • $\begingroup$ @Bas ... I would like to help you, but how could be your Q answered with given info you gave us? It still works for me with manifold objects in blender 4.+ ... so you would have to share your objects ... there are of course cases for complex shapes it can fails, but if you try Cube and Plane (as seen in my answer) I guess you can see it is working. So if it is not working for your objects, she issue lays there. Since I don't have a clue how they look like I can't help. Sorry $\endgroup$
    – vklidu
    Commented Apr 3 at 9:44

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