Tire sealant is used in road biking, mountain biking, and triathlon to help prevent flat tires. Though it adds weight to the wheel and tire combo, and triathletes are very much against added weight, tire sealant is becoming more popular in the triathlon world since the risk versus benefit of flatting versus saving time can lean towards this added protection. Tire sealant especially makes sense for city commuters, when weight and speed aren't a main criteria, and certainly cycling flat free month after month to and from work is important. The main manufacturers of tire sealant include: Stan's, Slime, Caffelatex, and Tufo. Caffelatex makes a product which allows cyclists to convert their clincher wheels into a tubeless setup by applying their product as a sealant inside clincher tires. Pitstop is a tire sealant product that is popular for those riding tubular tires - instead of having to tear off the entire tire, which is not only time-consuming but a finger buster as well, Pitstop and similar products can be squirted inside the tubular tire, the tire spun a few rotations, then reinflated for a much faster repair. This is especially true for triathletes on the go - pro riders in the peleton wouldn't need tire sealant since they will simply get a wheel swap from their team car. Tire sealants can be used with both butyl and latex tubes. However, you'll want to read the manufacturer instructions in that regard to make sure that the tire sealant you are buying matches up with the inner tube you intend to use. In the mountain biking world, tire sealants make a lot of sense, since the added weight proportionately won't make as crucial big difference as it does in the road cycling world. One common complaint about most tire sealants is that when a tire flats, this goopy stuff squirts out or oozes out of the tube, often creating a mess on both the wheel and tire. When inflating a tire with tire sealant inside, it's advisable to spin the wheel first, and then position the valve at 12 o'clock before airing up. An alternative to tire sealants is to use tire liners, which are strips of plastic, fabric, or other material placed inside a tire and meant to deflect thorns, burrs, and other very small sharp objects from puncturing the tube. The ultimate protection is both tire liners and tire sealant used in conjunction with one another.