This is premium 100% Cotton yo-yo string. Zeekio Yo-Yo String is available in packs of 10, 20, 100, or 1000 and comes in strong, vibrant colors. About Yo-Yo String-- Yo-yo string usually comes in one of three materials: Cotton: basic yo-yo string that comes with many yo-yos Slick: blend of 50% cotton and 50% polyester or nylon. Slick is a bit heavier than straight cotton and are more durable. Type 6 or 8 Polyester: 100% polyester string is a bit heavier, and a bit more flexible than slick. It is more durable and both Slick and Cotton. Yo-yo string also comes in different thicknesses. The Type is determined by the number of threads used to create the string. Commonly used string types are Type 9, Type 8, and Type 6. Type 6: is 6 threads (3 twisted pairs) Type 8: is 8 threads (4 twisted pairs) Type 9: is 9 threads (3 twisted twice) Generally Cotton string is Type 6 or Type 9. Generally Polyester is Type 8 Slick 6 is 50% Polyester, 50% Cotton Type 6 and usually only comes in lime or white. Slick 8 is 50% Polyester, 50% Cotton Type 8 and usually only comes in blue or white. Yo-yo string should be changed periodically. Manufacturers generally recommend changing the string after about 30 minutes of play time, or if the string becomes frayed. Non-bearing yo-yos will wear out the string quicker.