Flexible waterproof panel...?

[anders07]

I am going to construct a vaulted ceiling in a steam sauna and had thought that there are bendable boards, like those with XPS filling between two fiberglass layers...
Now I can't find anything like that (except Woody.se, but they say it's discontinued).

Is it really the case that it no longer exists?

How should I then construct my ceiling...?
Cut narrow strips of wet room boards...?

 

[RiKr]

Regular plaster should work if it's to be painted afterwards, right? Moisten it for a while before installation so it can be bent during installation.

 

[Plupp 405730]

Cement-based boards like minerit or similar are available from 6mm and thicker.

 

[anders07]

Regular plasterboard should work if it's going to be painted afterward, right? Moisten it for a while before installation so it can be bent during installation.

It's inside a steam sauna, so there needs to be a waterproofing layer on the ceiling as well. I preferably want to use wetroom board or something like wetroom plasterboard...

 

[Vante]

I used wet room gypsum that I scored on the back so it could be snapped in place.