I'm looking for the FAR reference as it pertains to normal category aircraft's interior requirements. I dug around this morning some but couldn't find anything specific. Specifically I want to rip out my old headliner and insulation and go back with a utility type interior of bare metal and fresh paint. However, I've heard, read and seen a bunch of contradicting information on the subject. Some say that's prohibited and must have some type of foam over the metal (like selkirk).

I'm sure some of you have gone down this wormhole previously and if so, I would be curious as to your thoughts/opinions as well as the basis for such modifications. Thanks in advance for any insight.

Find the TCDS for your airplane serial number and see if it says anything about interior components. Check your POH and see if it says anything specifically about the interior. If so you'll need to keep those intact without a Field Approval, STC, or perhaps an A&P sign off. Then if you aren't changing the structural integrity, or the way things operate, or the flight characteristics, or affecting the airworthiness, or changing the W&B or COG, remove away. It's adding things, like different flooring material, different seat material, etc that can be problematic because is has to pass burn tests among other things. Selkirk foam is nice in a utility interior because it helps quiet the plane and keeps larger areas of the skin from oil canning.

It depends on what regulations the aircraft was certified under.
John