Are there FAA regulations requiring insulation on passenger aircraft?

The KC-135 I was on didn't have any of the plastic paneling or insulation, exposed pipes and wires everywhere!

Is there any regulatory reason why a passenger or cargo carrier couldn't operate commercially like this?

With AA doing everything they can to shed weight, I wouldn't be surprised...

Please only respond if you have an answer, not a comment about the inherent stupidity of me or my post, thank you.