Why dose this model look such empty pipe?
#Why dose this model look such a empty pipe?
warped tundra
The magical words are backface culling. The faces on the other side of the pipe are pointing away from you, so the engine believes they aren't visible and doesn't render them.
warped tundra
So, imagine you have something like a ball. Then you'll never see any of the faces of the object that point away from you, because there's always some face pointing at you that hide them. And technically, it's the same thing here; the inside of the pipe that you see should be facing towards you. So as an optimization, the rendering engine chooses not to render those faces that point away from you.
The 'problem' here is that if that were a real pipe, it would have some thickness and there would be inside faces pointing at you, but the one you've modeled is only a single layer.
The act of not rendering the sides facing away from you is backface culling.
warped tundra
The 'right' way to fix it is to put an inside layer on your pipe that faces the correct way (ideally along with some 'o' shaped caps to cover any gaps at the ends). Blender can show you when you have sides facing the wrong way, too; if you look at https://cgian.com/2022/02/how-to-fixed-face-orientation-and-flip-normals it'll show you the menu option for showing the orientation of faces.
You don't want to use the flip tools here because then you'll have the same problem on the outside of the pipe instead of the inside, but that article should show you where to see.
toxic flume
Thank you.