Originally Posted by the homealien
Slime is the trade name for a glue that they put on the inside of the tubes. Theory is that it will start to ooze out through any puncture and quickly reseal the wound. My friend swears by it for mountain biking through the cactus needles in Arizona. He says if you get a flat you just pull the sharp thing out, spin the wheel to fling the slime to the outside of the tube, and pump it back up. That said, it makes the inside of the tire pretty nasty through repeated punctures, and I've seen them blow out and cover my friend in, well, slime. Some people love 'em, some people hate 'em.
Yep, I'm a lover not a flat changer. I use these tubes in all my bikes, even my roadie 700c - 23 tires. They work, sometimes I see a bit of the bright green stuff on the tire tread, indicating a puncture, but no significant air loss. You have to keep the valve clean though, if the green slime leaks out the valve while adding air, you need to wipe it off well, or it will glue the valve.