a concentrate of technology, incredibly solid and reactive

Keen is the narrowest string created by String Project.

The cobalt-blue exterior hides a very narrow section, 1.18 mms, but just as strong as any other.

The composition is a concentrated technological blend, a mixture of 5 different materials that make it incredibly solid and reactive after a snapback.


With its sensitive and powerful qualities, Keen increases the ability for spinning during the game, creating a natural connection with the ball and multiplied effect of power and rotation.

Its narrow calibre gives the right feel to tame thrust and to perceive the ball at its best when on the head of the racket, with a notable natural control over the direction of the shot.



Slender but enduring, Keen yields very well on control-based rackets and manages to enhance and simplify the player’s performance when in use.




Soft and elastic it also manages to protect the arm on impact.


Power: 7,5
Control: 7,5
Spin: 9,5
Comfort: 8,5
Stability: 7
Tension Loss: 9
Resilience Peak: 8,5


Static Stiffness 15-20Kg : 0,80 Kg/mm
Static Stiffness 20-25Kg : 0,80 Kg/mm

Dynamic Stiffness : 230 g/mm

Data taken from tests published by Pro-t-one of Eng. G. Medri


Material: Co-Poly with two differetn material including an elastic fiber and treated in alfa olefine

Manufatory Process: Multiple Heating  + Alfa Olefin + Liquid Wax

Section & Caliber: Circular 1.18mm (18)

Color: Blue

Laboratoty Test

  • Laboratory tests perfomed by Eng. Gabriele Medri of Pro t one (PDF)



Test on Court

  • Court Review performed by Eng. Gabriele Medri of Pro t one (PDF)
  • Court Review performed by Fabio Ferro of (Link)


Suggestions for use

We recommend to string the usual tension and to stay in the range of best performance of the string, 18-22 Kg, to maintain the characteristics of power and comfort of play.