[quanto]

There 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.

[fyrn_]

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..

[Iulioh]

While metal printing is attainable..it generally produce shit, surface quality wise. You still need to CNC that if you want a surface roughness not measured in mm

And is not like a 5axis could not produce these fan geometries from a block

[HPsquared]

Do they add glass fibers, I wonder. That's a way to make plastic stiffer but it's a bit harder to make.

[throwaway85825]

They definitely add something. Noctua has a different texture and grain.

[alex43578]

Hopefully not - I’d hate the idea of my fan shedding glass fibers right into the exhaust of my PC and onwards into my office.

[AlotOfReading]

Shedding is not a significant concern. You almost certainly use glass fiber reinforced plastics in products like your car and power tools.