The complex string structure mentioned in the tennis string refers not to the section structure of the tennis string, but to the string-through structure. Usually, the stronger string is worn on the vertical string, and then the nylon string or natural gut string with good feeling is worn on the horizontal string. This string-through structure is not only durable, but also has good ball feeling.

Polyester string polyester is another durable ball string material, which is wrapped with a layer of polyethylene material outside many nylon strings to make them integrated. Nowadays, more and more professional players have used the strings made of this material. However, the polyethylene material itself loses its elasticity faster than other artificial strings, so it is often used by leisure players mixed with Kevela strings.