Ontrack Gravel TPU Inner Tube 700X32-45C 48mmTPU standing for Thermoplastic Polyurethane, a flexible plastic with an inherently low weight. The highly elastic TPU bicycle tubes raise performance to levels previously unreached with either butyl or latex while returning a further reduction in punctures, and increasing air retention. Suppose you are a rider who seeks the ultimate in performance and appreciates the simplicity and hassle free installation and maintenance of a tube type system.