Spandex is the abbreviation of polyurethane fiber, which is an elastic fiber. Generally, spandex is composed of multiple filaments, usually 10 days per filament, and now it has 15 days per filament or even 20D/ days per filament. 

The smaller the theoretical number, the better the evenness of yarn. Because of the less chance of overlapping, the DMAC produced by dry spinning is harmful to human liver. Generally, the content of DMAC in 10 days per filament is controlled at 0.5mg/kg, while that in 15 days per filament is 0.7mg/kg, which exceeds the standard. When producing Spandex, special attention should be paid to the coiling tension, count on the bobbin, breaking strength, breaking elongation, forming degree, oil adhesion, elastic recovery rate, etc. 

These problems directly affect knitting, especially in the production of single-sided fabrics by knitting.