Designed to perform on the track or the trail. Whether you ride hard-pack or sand, the natural rubber compounds of the BikeMaster Heavy-Duty tubes are durable. With increased wall thickness, these tubes provide better puncture and pinch flat protection to keep you riding. Seamless construction with increased wall thickness. Natural rubber compound with reinforced valve stems. Individually packaged with the part number and size on each box. Heavy Duty 80/100-21