alt Hacker NewsThere could be geometrically tiny optimizations that lead to an outsized impact in noise and flow by turbulence reduction. While optimizing an impeller with computational FSI (fluid structure interaction) is not as hard as before, it still is not trivial. And it's these (perhaps small) optimizations that justify Noctua being 5x more expensive than generic black fan.
I believe the tolerances to the fan housing (which reduces turbulence and thus noise), and the the material stiffness needed for that small tolerance, are the alleged reason there are few copycats. Supposedly getting plastic that rigid is hard. I've tried to find hard numbers and validate that claim, but I wasn't able to. Would probably have to measure an actual noctua fan blade to know. On the other hand, metal printing is attainable now..