TPI = Threads per inch
Tire casing is the fabric that the rubber compound adheres to. The fabric of the casing can be made in varying thickness and threads per inch (TPI). Generally, the higher the TPI number, the suppler the tire sidewall will feel and flex. This means a more comfortable ride compared to that of a lower TPI casing. The casings can be treated and reinforced with various materials in order to achieve different degrees of puncture resistance and ride qualities.