Defining the outside of a face?

I am fairly new to blender, I started using it about a month and a half ago, have a few models done, but haven’t textured anything. In my most recent model I encountered a odd phenomenon where after exporting the model as a fbx and importing it into my game, a bunch of surfaces were not rendered. However you can view these surfaces if you go inside the model. My question is, what is this called, and how do you define which side of a face is rendered?

Looking back at the model in blender, the parts are two slightly different colors.

You can display the face normals in edit mode

Options to display and flip face normals see


Thank you for the prompt reply, thats exactly what I was looking for. Now is there a way to mark solved or does that not a function of this forum.

The “problem” you are experiencing is called backface culling. The slight variation in display color within blender because your faces are facing different directions. To fix this, highlight your mesh in edit mode and press CTRL+N. If this does not fix it all, you will have to manually flip the faces by highlighting the flipped face and pressing w > flip normals.

Thank you, I had it resolved but for some reason it seems that only 50% of what I try and post ends up on this fourm.