I've had good firsthand experience with "Slime", the bright green stuff. Worked once for a 3-hour harescramble. I saw this stuff in the mountain bike world first. Supposedly works by forming a fiberous "patch" whenever it contacts outside air. However it works, I give it a thumbs-up.:)
I also use the green Slime in my bike tires. I also use it in the tires of my lawn mowers which used to get get alot of flats. I've put it in mower tires that were already flat and the hole was sealed, problem solved. I never had to take the tire off to plug it. Whenever I change my motorcycle tires I get new tubes and put the slime in before the tire ever goes on the bike. I haven't had a flat in the 3 years I've been back riding.