Pneumatic tires are awesome, and the original rubber tires were solid and completely flat-proof, but riders have always asked for a middle ground of comfort and flat proof performance. Hutchinson tires has introduced the Serenity system of absolutely flat proof tires consisting of a microcell foam donut inside of the tire that approximates 50 psi and while not the easiest to install won’t leave you in lurch with an unrideable flat. 20, 24 and 26″ and 700c versions. These are the same folks designing run-flat tires for the military and government applications, so if anyone can make it work it might just be this French company. Pricing and ultimate availability is yet to be determined.