Apart from random videos on YouTube, are there any particularly good books or dvds that go through the art of twisting up balloons? I'm new to this but I'd like to know more about the science behind why x many twists, best practices, how to make the balloons last longer than a day or so (is that just a balloon quality issue?)

Open to books, dvds, other link reccomendations. I got into this specifically because I needed to replace my son's dinosaur balloon he got from another magician. Turned out it was a lot of fun and I'd like to start incorporating some balloon tying into my act for kids (some really great reccomendations here already)

You can get this at Penguin: https://www.penguinmagic.com/p/S16578

For beginners, you can't go wrong with Tricky the Clown Balloon Sculpture Vhs (no longer available but someone converted it to digital for Youtube):

https://www.youtube.com/watch?v=Jsf9Y1Xjaho

Google tricky the clown dvd. They’re out there. Like $10bucks.

I did this course and it was very helpful for me. Paid for itself within a night or two.
https://www.balloon-twisting-school.com/......_courses