I tried out using organza ribbon to make tails. Organza is the semi-see-through stuff that Robert Brasington uses on some of his SLK tails, but I got it in ribbon form. It's ribbon, so the edges aren't cut or raw. It's lightweight, available in black, white, and a variety of colors, and available in >50' lengths. I think mine are 2" wide by 75' long, but they may be 1.5" wide if I remembered wrong.
HOWEVER, I wasn't too happy with their skywriting effect, or rather, lack thereof. The tails wouldn't follow the path of the kite very well. What I mean is, say you flew the kite around in a small circle a few times. I would expect the tail to spiral around downwind of the kite such that you could see the circles you just flew, leaving a big open area in the middle about the size of the circle flown. Unfortunately, with the organza ribbon tails, the end of the tail stays much more toward the center of the circle. The end of the tail doesn't "follow" as well. My guess is the material is so sheer/porous that there is some dampening effect going on and the end of the tail moves much less than the part connected to the kite. I also thought 75' was a bit long but haven't cut them shorter yet. I haven't flown with them much.
Maybe there is some other kind of ribbon out there that is solid enough to have better skywriting effect but not too heavy. I haven't found it yet.