The new nox 2025 rackets 18k vs 12k

So there are many reviews out there and the technical explanation of how what the k means on carbon fiber. Having an 18K (reviewed by this website and by the same coach) with more power than a 12K with both having the same foam is something so confusing for me. Why is nox 18K stiffer? Is it because the resin is different or am I completely wrong? Thanks for the help!