Why have capacitors improved so much over the years?

If they have, and I wouldn’t doubt that they have, it is likely due to more precise computer aided design and robotic manufacture.

I've been modding for perhaps twenty years now, IME, both film and electrolytics have improved, I presume for all the reasons above. Really, very few choices years ago with boutique caps, most were general use variety. As I recall, the first audiophile grade film caps I used were from VH Audio, Duelund, Jantzen, Mundorf, seems like they all came to market in about the same range of time. So many brand choices today, way more values, voltages, metallurgy  available today. I've yet to hear a bad boutique film cap in my mod projects, only sq issue has been less than preferred colorations, large physical size sometimes makes fitting a chore.

@troidelover1499

It is still just salt

not sure you'd have a lot of chefs and gourmets in agreement... 

@jond - NOS capacitors, huh? Uh oh, another crazy rabbit hole! 

Why have capacitors improved so much over the years?

Not so with all caps

And as far as non-polarized (plastics etc) coupling caps go, the BEST CAP IS NO CAP, if the circuit allows for it to trim out any dc offset manually, or a simple dc servo can be installed. (direct coupled always sound better) but not all circuits can be dc coupled

As for polarized big or small electrolytic power supply caps go, some quality makes NOS (new old stock) can be very good, but very important they need to be "conditioned" first using an ac variac, over a couple of hours and bought up from zero very slowly to their max voltage.

Cheers George

Vintage Japan Man collectors pay their weight in Gold Pressed Latinum for formed and working 50’s production TCC Metal and Super Metalpack paper in oils.....