The NRG² was designed with a special purpose in mind: to be the engine of the racket! This is the primary meaning of NRG², the most powerful string in the range. A specific construction of more than 1200 microfilaments, made of Elastyl (12% more elastic than standard polyamide). Impregnated with 400 polyurethane to generate power and comfort. And finally, the exclusive S.P.L surface treatment to provide slip and effective snap back so you don't have to re-string during play. In 1.32 gauge, it is the guarantee to gain in resistance. Welcome to NRG²! String made in France. PU 400: 400% elasticity for great comfort and dynamic performance. Elastyl fibres (100%): +12% elasticity compared to standard PA. Provides enormous elasticity for maximum power. S.P.L final coating Anti-abrasion coating for more resistance. BEST SELLER USA Among the top 10 best sellers for over 20 years among specialists.