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I watched this tutorial and they made a bedroom floor by creating a plane and adding thickness modifier.

I don't get why they would use that instead of just extruding it up along the z-axis?

Only difference I noticed is the thickness floor only has a top face on edit mode, but extruding it creates faces on all sides.

Does it matter for creating models?

Or as long as you don't need extra faces, then thickness would make sense?

Is there a benefit for using either or?

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    $\begingroup$ I think Solidify modifier gives the same result as Extrude Faces Along Normals, except a modifier doesn't create any real new faces, so it allows you to change the topology and thickness more easily $\endgroup$
    – moonboots
    Commented Apr 6, 2022 at 7:37
  • $\begingroup$ so if you were to create a thick plane for a bedroom floor, is there any performance benefits for using either or? or it's just preference? $\endgroup$
    – makerbaker
    Commented Apr 6, 2022 at 7:44
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    $\begingroup$ It depends on you needs, are you supposed to see the thickness of your floor? If not, you don't even need thickness. If you need thickness, you can use either extrude or Solidify. That said, you can unwrap real topology, but you can't unwrap the sides of an object with Solidify (you can give a different material for the sides though) $\endgroup$
    – moonboots
    Commented Apr 6, 2022 at 7:48
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    $\begingroup$ The thickness modifier is more computationally heavy (it needs to compute the geometry every time you change the underlying geometry) but the file size will be lighter because the vertices aren't actually stored anywhere, they're generated at runtime. In terms of RAM usage I guess it's pretty much the same thing. Another benefit as mentioned by moonboots is that if at some point you want your slab to be 0.4 units thick instead of 0.2 units thick, you just have to adjust the slider in the modifier properties $\endgroup$
    – Gorgious
    Commented Apr 6, 2022 at 7:48

2 Answers 2

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The reason is that extrude (red) makes a hole and you must create another face by hand, whereas solidify modifier (blue) doesn't. As long as your model has all the faces it makes no difference as you can't see what's inside. Still, when you remove some faces as in this example...
enter image description here

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The Solidify modifier gives the same result as the Extrude Faces Along Normals operation, except a modifier doesn't create any real new faces, so it allows you to change the topology and thickness more easily, and also, as Gorgious points it out, it makes the object lighter.

With the Solidify modifier you can give a different material to the extruded faces, you can even give its own material to the rims, but contrary to a real extruded object you can't unwrap these faces, so it's a limitation.

That said, for a floor, if you don't need to show its thickness, you don't need to extrude it or to give it a Solidify modifier, a simple plane is enough.

For an object like a shirt, the Solidify modifier is very useful as it gives thickness to your object without making it heavier, and you can easily rework the topology. You don't need to apply it, just put it after the Armature modifier if it's for an animated character.

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