Method 1. Combustion method. When the cotton burns, the flame is smooth, take a small amount of fiber and ignite it, and observe the ash left by it. If it is loose, the cotton will be broken when twisted; on the contrary, if it melts first, it forms agglomerated adhesion together. The solid one is polyester. Cotton fiber: close to the flame: non-shrinking and non-melting; contacting the flame: burning rapidly; leaving the flame: continuing to burn; smell: the smell of burning paper; residue characteristics: a small amount of gray-black or gray-white ash