Li-Ning's No.7 Boost is a premium staple for your prized racket. An ultra-durable string, it promises super durability and a soft hitting feeling. The core of the string is made of high polymer and nylon filament. The outer part of the string is made of heat resistant and high-intensity nylon. This string comes engineered with Li-Ning's Deep-Re-Dipping technology that helps improve durability and prevent loss of tension. The string is coated with compound nylon that gives you a fantastic hitting feeling.