Tire sealants are liquids that are put inside a bike tube which, ideally, can seal small punctures. When a puncture occurs, the compressed air inside the tire forces the sealant through the hole at high velocity. When it contacts the low-pressure air, it coagulates to form a seal. For holes up to 2mm or so, which is most punctures due to glass, thorns, wire and small tacks, the sealant is very effective. (from bicycle tires.com).
Sealant tubes are very convienient for commuters who don't have time to change a flat. If the sealant is already inside your tire, simply remove the cause of the flat (glass, nail, etc.) reinflate, and you are on your way.
To learn more, check Tufo, Vittoria, and slime sealant.
Posted by Attorney Clayton Griessmeyer-Wisconsin Bicycle Accident Lawyer