ᐅ XPS with the same thermal conductivity – different thermal resistance (R-value)

Hello everyone,

On our construction site, we have different XPS boards from BASF for the foundation slab:
one is Styrodur 4000 CS, 80 mm (3.1 inches) thick, with a thermal conductivity of 0.035 W/(m·K) and a thermal resistance of 2.25 m²·K/W,
and the other is Styrodur 4000 CS, 80 mm (3.1 inches) thick, with the same thermal conductivity of 0.035 W/(m·K) but a thermal resistance of 2.30 m²·K/W.

Two questions:
1) I assume that the difference between 2.25 and 2.30 is so marginal that mixing these boards together is fine and won’t be noticeable, right?

2) How is this possible? I thought that if the thermal resistance is higher/lower, the thermal conductivity should be lower/higher accordingly. How can one value be the same while the other is slightly higher?

Thanks for your answers.

Best regards

Does no one here have any idea??

annab377 schrieb:
1) I strongly assume that the difference between 2.25 and 2.30 is so minimal that the two types of boards can definitely be mixed together without any noticeable effect, right?

Correct

And how can such differences occur? Isn’t one dependent on the other?

Interesting, theoretical question. Wasn't there a physicist active in this forum as well?

Have you ever asked BASF? They should be able to explain it. If they respond.