Tufo's 'tubular clinchers' have proved to be popular with time-triallists. They're essentially tubulars with a hooked bead to make them compatible with most hooked, narrow clincher rims.
Where on normal tyres the rim becomes a stressed member, when Tufos are fitted the rim serves only to clinch the hooked bead. This means that they can be operated at pressures of up to 160psi without risk of blowing off the rim.
While tubular tyres are easily repairable by detaching the threads, the Tufo's carcass is moulded, rendering it non-user-serviceable. Punctures are taken care of using a rubber solution that's installed through the valve hole prior to use.
The solution does its job in most cases, except for particularly heavy pinch punctures. Large thorns can also present a problem. Resistance to punctures is further strengthened with the use of 120TPI casing and a rubber cord composite between tread and carcass. The S3 is a middle-of-the-range choice, and is the best balance of performance and value for money if you're after this kind of tyre.