Luxhaus and competitors - diffusion-open wall

In the USA, construction is done like this. Wood frame, insulation, OSB, and drywall. House finished.

Breathable walls are a marketing gimmick. Don't fall for that nonsense.

I would like to ask a question regarding this: For our new house, we have the choice between "diffusion-open with wood fiber board" and "diffusion-closed with polystyrene." (I can gladly provide the exact wall structure for both cases if necessary.) The price difference is 5,440.00 including VAT for our two-story house, 9.40 m x 9.40 m.

Is our current choice of "diffusion-open with wood fiber board," which we can still revoke, a good one, or can we also do without it?

By the way, we are building without a ventilation system.

I can gladly provide the exact wall structure in both cases if necessary.

Yes, please.

Yes, please.

Thank you for your interest. The two descriptions are attached. I photographed them from the construction performance description and hope that I am not violating any copyrights.

By the way, we are building without a ventilation system.

Not diffusion-open with ventilation makes EXTREMELY much more sense than diffusion-open without ventilation. At least an exhaust fan in the bathroom would definitely be necessary for me.

I would prefer a ventilated curtain facade. And I believe OSB glued at the joints is no longer considered vapor-permeable. But maybe a real expert can say more about that than a layperson who has construction done.

...just wondering... what do you think is diffusing there?