Styrodur - the ideal insulation material for everything?

Hello!
Due to new construction plans, I have been reading up on insulation materials.
Therefore, I now know that the insulation material should preferably be separated from the indoor air by a foil so that no moisture condenses in or on it as soon as the dew point shifts there.
I have also gained the impression that an insulation material should ideally be hydrophobic, meaning it should not absorb moisture. Am I correct in this assessment?
So ideally, it should be a closed-cell insulation material, and thus I quickly came across Styrodur.
This is now also being applied to the inner shell, on the Ytong blocks, and it is also intended to be used under the screed.
I am now considering whether I can also use Styrodur for the roof because of its ideal properties....

Styrodur is a brand name, like Tempo, and not primarily a building material. What you probably mean is XPS, which is used under the floor slab and as perimeter insulation. XPS also doesn't have "ideal" properties, but properties that are exactly suited for this purpose. Under no circumstances does that stuff belong on interior walls or on the roof... I'm starting to seriously wonder if you only want to troll with your threads..

I am an extremely balanced person and therefore have no desire for disputes... so let's stick to the topic:

WHY doesn't Styrodur belong on the inner shell or under the roof?

(By the way, it seems my builder also wants to "troll," because he is currently installing Styrodur on my inner shell... a company with a 40-year history...)

Lumpi: If I knew everything like you, then I wouldn't need to be registered in any forum.

Fire away... Lumpi,... just a little joke.

We insulate our cold roof, meaning the upper floor concrete ceiling from above with EPS. Of course not the facade, but there is nothing wrong with that. At least not with me :p

What do you mean by Innnenschale? Above you write inside on the Ytong blocks. Whoever sticks insulation on Ytong blocks inside, whether XPS, EPS, or MW, doesn't know what they are doing. If they really do that, well then congratulations. Polyurethane belongs on the roof, EPS is economical on ceilings. On the outside(!) of the walls you can do all kinds of things, economically it is EPS or SW, but definitely not XPS.

It's not as simple as you think. The insulation material can very well be open-pored; it just has to be able to release moisture again. You can also google vapor diffusion.