The Mr. Tuffy Purple Tire Liners (2) (29x2.00-2.35-2.5) provides a protective layer between the outer tire and inner tube. It is made from a durable, lightweight Urethane. When a thorn or piece of glass attempts to penetrate the Mr. Tuffy liner it comes up against a surface that is both hard and elastic. The object pushes against the surface which gives way while resisting initial penetration.