In blender click on the down arrow next to Viewport overlay icon(top right corner on the 3D view), then click on the “Face Orientation” check box. After that you will see your model in blue and red. Red means you see the back side of the face, if you see the red faces in Unreal Engine you will see thrugh them. Usualy there is a few step that can fix your mesh automaticly. Select your mesh in Object mode → ctrl+A → rotation and scale. If it’s not fixing all you normals probleme, go to edit mode, hit A to select all of the face, then Shift+N it will recalculate your face normals. Most of the cases it will fix all the faces, if not, select the bad faces, and hit shift+N, and in the bottom left corner check the “inside” check box. In the future, don’t forget, the first step(ctrl+A ->rotation and scale) before export, because the exporter automaticaly applying the rotain and scale, and in Unreal Engine, the result will be bad even if the normals looks good in Blender.
2 Likes