Continental MTB Inner Tubes - 42mm Presta Valve (Pack of 2 BULK) - Continental bike tubes are constructed of durable butyl rubber and are 100 percent inspected to ensure quality. The tubes are seamless and vulcanized for uniform roundness and improved reliability. Material: Butyl tubes with renowned Continental quality - Durability: Each and every inner tube passes a stringent 100% quality control inspection - Design: Seamless construction, with a mold-cured vulcanization, to ensure uniform roundness and give a smooth ride and handling.