This is premium 100% Cotton (type 6) 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. 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.