The NRG² was designed with a particular purpose: to be the engine of the racquet! This is the 1st direction of the NRG², the most powerful string in the range. A specific construction of more than 1200 microfilaments, composed of Elastyl (12% more elastic than standard polyamide). Impregnated to the heart with polyurethane 400 to generate power and comfort. And finally the exclusive surface treatment: the SPL to provide slipperiness and effective "snap back" so as not to have to put the strings back in place during the game. In 1.32 gauge, it is the guarantee of gaining resistance . Welcome to NRG²! String made in France. PU 400: 400% elasticity for great comfort and dynamic performance. Elastyl fibers (100%): +12% elasticity compared to standard PA. Provides enormous elasticity for maximum power. SPL final coating Anti-abrasion coating for more resistance. BEST SELLER USA Among the top 10 best sellers for more than 20 years among specialists.