Ok so I'm making an unturned mod and I made the gun model in blender and exported it into unity as an fbx. Now when I exported it and opened it in Unity, the model looked destroyed and many faces of the gun was missing. I tried switching shaders of the material but to no avail. I cant figure out if its something in Unity or how I exported the model through Blender.
If you aren't sure if your model has inverted normals, you can always check them in Blender.
Hit N to open the properties panel, then go to "Mesh Display" and select "Display Face Normals as Line". This option reveals the normals in your model as a line. The lines should be visible as shown in the picture below (yellow arrows show correct normals, blue arrows show inverted normals. You will only see the lines)
To recalculate the normals for your entire model, tab into edit mode and hit Ctrl+N. If that doesn't change the normals on the affected faces, select those faces, go to the 3D Viewport Menu - "Mesh" - "Normals" - "Flip Normals".
All you need to do is invert normals to right direction.
In edit mode: Easiest way is select all faces by "A" > recalculate by "CTRL+N". This work in most cases. Usally does not work in non-closed/un-manifold meshes
Second way is manually select normals which you need invert and press "SPACE" > start typing "flip normals" > "Enter".