This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
From Bob Kaplow:
...folding and pleating the streamer is legal. In fact it's standard
practice. But quarter mil and even half mil parachute mylar just
doesn't pleat well. For best results, you need to find about 1 mil
mylar. The old Ed LaCroix Apogee used to sell it. I don't know of a
current source. If any one else does, please say so.
The heavier mylar doesn't tear as easy as the quarter mil stuff. What
I do with either mylar or tissue (I still use drafting tissue for most
of my competition streamers) is to tape the Kevlar to the streamer at
a 45 degree angle from one corner. Use the magic yellow tape that Ring
Rocketry sells. I tie several knots in the Kevlar first, to keep it
from pulling out, and if possible, fray the Kevlar end to increase the
I also reinforce both the leading edge and the side of the streamer at
the attachment point with another piece of tape. And for the tissue, I
also put a piece of tape on the BACK side, to prevent it from tearing
through the tissue.
I use a very long Kevlar shock cord, longer than the streamer. I also
bungee it with a piece of sewing elastic that is designed to break in
use. That absorbs the ejection energy. Replace after every flight.