When yo-yos caught on starting in 1928, silk yo-yo string (see the Flores yo-yo exhibit) was sold besides cotton yo-yo string. With time, cotton strings became the standard for all fixed axle wooden yo-yos. Even after the introduction of metal axle yo-yos, cotton string was still used. It wasn't until the 90s that new string formulations and materials were introduced that further optimized play and string life.
