Decorating celotex

You can. It's about 3x the price of regular rockwool and fairly hard to get hold of. I concluded it was easier to just get some mylar film and staple it around some rockwool. The mylar is used for hydroponics - this kind of thing:

also easier to handle, but also to fix to vertical surfaces - can be stapled etc.

That could cause interstitial condensation inside the insulation. The plastic wrapping used by space blanket has (or used to have) holes to allow water vapour to escape.

Mine was the dirt cheap subsidised-by-leccy company stuff from B&Q, it does seem harder to find now though, not sure why, it was worth it not to have to touch the itchy stuff.

I got an abscess the size of a chickens egg on my neck from a shard of rockwool once.

Full of pus. Needed draining daily and antibiotics for a week

Surprising. I used about 20m2 of 150mm Rockwool here. Mostly at ceiling height to segregate the underfloor heating circuits. Mostly without any form of protection.

I have an idea *Earthwool* is actually glass fibre!