If you are a professional who is installing insulation all the time? You absolutely need that mask.

If you're a flipper who buys a new house every year or two and usually replaces the insulation? You should wear a mask.

A homeowner who installs it once, maybe twice in their lifetime? Eh. A lot of PPE mandates are about doing it often and professionally where you can get a lot of exposure. Or if you already are at risk. If you have respiratory issues then if course you should wear a mask. If you have healthy lungs and plan to do this task just once in your lifetime, just having decent ventilation and not shoving your face in it is fine.

I'd wear gloves, but more because the rafters probably have splinters and rusted old nails or staples or whatever. The skin irritation from fiberglass lasts like a day or two and doesn't have any long-term impacts, but I also find gloves aren't as inconvenient as masks.

Eye protection is a must. I don't mess with that.

Or you can just pay the extra money for Rock Wool and get all the other benefits that come with that too.

Is there loose or exposed insulation up there?

I’m in no way an expert, but I would think that your insulation won’t be shedding much into the air once it’s in place.

I’d wear a mask, gloves, and long clothes if I were going to touch or move it around though.

You know how sand on the beach is fine, but sand in a super windy dust storm stings like hell? Insulation is fine so long as nobody is actively touching it and spewing out bits. Probably shouldn’t be able to see it but it won’t kill ya.