Ceilings and joists

hello Lemmy,

Every little while I update you on my basement build as I encounter problems. I am pleased to tell you the city is out of our hair. We have gotten everything up to code.

So here is where things get weird. My roommate and I live down here in the basement. Our rooms don't have drywall or tile ceilings. Currently, our funds are exhausted, and I am not looking to pick a fight with the city over permitting with the ceilings. That's a someday kind of thing.

We would like a small modicum of noise privacy from each other though. Right now the walls go up to the top plate, and end at the joists. The joists are open, as illustrated.

I am thinking I put something in the joists. My thought was just to grab some faced fiber glass insulation, staple it in there, and cover up the other side with a piece cut out from a blanket. I was also thinking maybe some XPS, which would be easier to cut to size and shape around infrastructure. I'm worried about foam board's flammability. I was also checking around my options with various blanket types, finding wool to be a good option, and a welding blanket to be an option as well.

Am I insane? Are the words coming out of my mouth still making sense? Does anyone have any idea what I'm talking about? or any suggestions? Help would be appreciated.