It would be nice to have curtains that absorb street noise.
Some custom curtain tailors offer a fabric that claims to be soundproof. It’s a little pricey. Not absurdly pricey, but it’s also a bit hard to be confident that such thin fabrics can absorb much sound (they claim 20%).
I would prefer to try hacks. I’ve heard that thick furniture moving pads absorb sound well. I’ve also heard that fiberous fabrics can be effective. For the moment, I probably want to pass on edgy ideas like egg cartons. Maybe later on those. What fabrics are decent for reducing sound? Specifically, I’m wondering about carpets or painter’s drop cloths. Not the simple white canvas drop cloths, but the thicker drop cloths may out of recycled fabrics.
Sound insulation and sound absorbtion are two very different things.
Egg cartons are a myth. They do nothing for sound and only create a fire hazard.
Professionel recording rooms might have egg carton shaped foam to absorb sound instead of reflecting it. It has nothing to do with sound insulation. It does not stop the sound. It only stops the sound from reflecting, so that he microphone gets a clear signal without reverb. You can still hear the sound everywhere inside and outside the recording room.
To insulate your ears from sound, you use ear plugs.
Similarly, to insulate your apartment from sound, you basically need earplugs for your windows.