Players with long, fast strokes should love Yonex Poly Tour Fire - a round polyester monofilament that will keep your biggest strokes inside the lines. The feel is firm but nicely dampened, with a surprisingly low level of shock on off-center hits. Yonex has made this string with its unique Silicone Oil Infused Filament (SIF) Technology. This is a manufacturing process that reduces stringbed friction, enabling the strings to snap back with vicious force (resulting in heavy spin).