I am biased since I was the president of the company that sold Mr. Tuffy for 26 years. In testing, it stops 97% of puncture flats. Very important in the thorn states. I sold out last year. My old company no longer sells Mr. Tuffy, but has switched the brand name to STOP Flats 2. It is exactly the same product, just different packaging. The other folks are correct. Innertubes are not as hard resistant to thorns, glass etc. This is both because the urethane has a very high hardness on the surface, and also has great elasticity.