Runflat tyres are specially designed to be able to continue driving safely even after a puncture, usually for around 50 km. It is possible because of the self-supporting structure they have that keeps the shape of the tyre even with no air.Runflat tyres are usually a bit heavier and little less comfortable than regular tyres.
Pirelli P ZERO PZ4 is made in 338 sizes, which of them 5 are made in the RUNFLAT specification :