Although the timing belt is a common part of the engine, not all OEM and aftermarket timing belts are designed to be used on highly tuned turbo powered engines. The durability of the timing belt is greatly reduced with performance engines running at high RPM with aggressive camshafts, increased torque coming from the valve springs, extreme heat conditions from the larger turbos and more. 
TOMEI Reinforced Timing Belt is made by high saturated HNB-Rubber and reinforced glass core fiber.
The gear facing fabric is made from Aramid fiber instead of standard Nylon to slightly increase the tensile strength.
Everything is designed to make sure the camshafts are driven at the right valve timing even under severe conditions.