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.
Try searching for “sound absorbing window vents” or “accoustic trickle vents” or “silent air vent”.
I think they all use something that is called an air maze. The air (and sound) will travel through series of bends covered with foam so the sound will be blocked but not the air. This does make the airflow slow down so it needs a fan the make it go through.