The “durometer” of rubber is a measurement of its stickiness. A higher durometer means the rubber is less sticky. For example, rubber with a 40 shore A durometer is the type they use to make windshield wiper blades, because it’s soft and sticky enough to conform closely to glass. But bicycle tires made of such a sticky rubber wouldn’t last long on the open road. A 70 shore A durometer rubber is harder, not quite as slippery as the soles of your sneakers. We must be honest though, not many manufacturers list the durometer.