What material is kendama string made of? It’s just a single thread piece of string, not complicated like yoyo string, so if I have a roll of this lying around, I can use it. Is it nylon?
I have been looking for this answer too, and so far nothing has come up. I would think it would be the same kind of string that people use to make friendship bracelets, you know the string and beads kind of bracelets, however I am not sure about it. Hopefully someone can give you better insight. Good luck on your search. 
Can you use normal yo-yo string on a kendama?
I think I saw some guy do this at a kendama contest and he was like, “Wow, no more string burn from string tricks.”
I’ve heard some people try that, but the disadvantage to that is tension. After a while every time you hop the tama up the string bunches up and might get in the way. However if you keep the tension low I guess it could work, but it seems like a drag to constantly allow the string to unwind itself after a few tricks, however if you are patient enough to do that I suppose it is fine. 
It reminds me a lot of the string that is used to draw blinds for windows. Kind of slick and thicker than normal string, also using a different weave. I was thinking of checking Menards for blind cord or something similar.
Exactly!
Kendama string is stiffer and slicker than yoyo string. It also doesn’t have much bounce. Apparently, the material for blind cords is most commonly polyester. So it must be the weave itself. Or the type of polyester.