Single Covered Yarn: Wrapped by a single filament yarn, it can be divided into two specifications as Z twist and S-twist. Double Covered Yarn: Wrapped by two yarns in opposite directions. One is in S twist and the other is in Z twist. Different TPM will make various senses of touch. Polyester: 12D to 140D Nylon: 30D to 1200D Spandex: 20D to 420D Twist: 500TPM - 2800TPM Stretch: High, Medium, Low