Challenge Tires are Handmade Tubular tire manufacturers as our casings are made of a quality cotton polyester thread called CoreSpun. A weave of Corespun allows us to obtain both supple and strong but light casing at the same time. Our production process avoids vulcanization, allowing materials to maintain their original supple ness and flexibility. The casings are mounted on rims and then inflated and the thread are slowly hand glued on them. Instead of being placed on casings which are subsequently inflated. This results in lower rolling resistance, increased comfort and a more precise handling of the bike. Additionally, a special fabric is placed between the tread and casing to increase resistance to puncture - PPS (Puncture Protection System). Challenge achieves comfort without performance compromise.