The Square-X is easily in our Top 3 best selling co-polys for its softness and incredible feel. Most players we know who played with rpm have switched to the Square-X not only because of the price but it's playability and durability. If you want a very soft co-poly which is easy on the arm; incredible feel and durable but less than half the cost of rpm...then switch to the Square-X. Made in Germany where only the best are made. Two Flat surfaces, mains/crosses, in contact with each other give extra durability, no notching and the string returns very quickly from any movement after hitting the ball. It measures 1.20mm across the flat sides and therefore plays like a much thinner string increasing power and control. We have only one word to describe this string: Unique! Note: The BLACK COLOR on this string does play SOFTER than the white so be sure to get the right color according to what you are looking for in a string. The white color has a crispier feel and a bit stiffer than the black color. Made in Germany where only the best tennis strings are made.