Bicycle inner tubes that contain a small-puncture-sealing slimy liquid may not be a new development in and of themselves, but Michelin has released a product that takes the concept a step further. The company's Protek Max tube not only contains a sealant, but is designed to compress when punctured to assist the self-sealing process.
The two things you'll notice about the Protek is that it has a square cross-section, and funny little bumps on its surface. The square shape helps align it within the tire casing and against the rim well, which Michelin says eases mounting and eliminates the twisting problems that can occur with traditional sausage-shaped tubes.
When the tube is fully inflated within the tire, its textured surface causes the rubber to compress instead of expand when under pressure. This means that the internal air pressure actually closes holes off, giving the sealant a better chance at taking care of them for good.
The tubes also are claimed to hold air longer – when tested against Michelin's self-sealing AIRSTOP tube, the Protek was said to maintain proper pressure for twice the amount of time.
Commuters and mountain bikers, but not road racers, can get a Protek Max to fit their tire. It is available in sizes of 700 x 35-47c (200 grams) and 26 x 1.4-2.125 inches (260 grams), with Presta or Shrader valves, for a suggested retail price of US$8.99.