Continental Cross Tubes are made of seamless butyl rubber and are individually tested for top quality. They're also heavier duty than standard tubes and perfect for the rough-and-tumble world that is cyclocross.
MICHELIN's Airstop name says it all. Their Airstop tubes use a proprietary butyl rubber that holds pressure longer so you won't have to top off your tires so much. These fine tubes are reinforced at the valve, too.