Some countries regard polyurethane containing more than 85% as the standard to distinguish spandex from other elastic fibers. In fact, the main difference between spandex and other elastic fibers (such as rubber yarn) is its performance:
The elongation at break is above 400%, and some reaches 600%;
The elastic recovery rate after 300% elongation is over 95%;
It has the strength 0.6--1.3cN / dtex required for textile processing;
Fineness range 22-6000dtex, even 10dtex;
Capable of high temperature setting and dyeing with polyester, nylon, cotton, etc.
It is also effective for someone to test the strength properties of unknown elastic fibers to determine whether they are spandex.