The slightly lighter feeling tyre! 

Slick-tread design,
120 TPI* 
KEVLAR FOLDABLE BEAD LIGHTWEIGHT 
20” x 2.1”: 543g (1.2lbs),
20” x 2.25”: 555g (1.22lbs) 
 
* more threads per inch than regular tires. 
results in lightweight structure with same sidewall strength