Objects only the backside is visibly rendered - Major Bug or my fault?

Hello there,
I have a strange problem here. i imported a couple of objects via Cinema 4D to Unity. Everything went smoothly. Now I have a pretty simple symbol basically a cylinder with a sphere at the end and this object behaves abnormal. I do not know if this a major bug or I am doing something wrong. I try to describe it. When I look at the cylinder only the backside is rendered as a closed surface. The front side appears as a mesh. So I basically can look INSIDE all those objects where the problem occurs.

Please tell me what I do wrong. Thanks!

Try reversing the normals in Cinema4d before you export.

Can you please tell me how to do that?
Thanks!

The surface normals of your object are reversed, best is to fix this in cinema 4d directly and then reimport.

A quick fix is to re-calculate the normals on import in unity (that’s an option in the asset importer inspector)

Cheers, Tommy