Air Covered Yarn (ACY) and Spandex Covered Yarn (SCY) are two types of yarn commonly used in the textile industry. While both have the capability to add stretch and elasticity to fabrics, they differ in terms of their construction, properties, and applications.    1. Construction:    - ACY: Air Covered Yarn is a type of yarn where a core yarn is wrapped with a filament yarn using compressed air. The wrapping process creates intermittent loops or bubbles of the filament yarn around the core.    - SCY: Spandex Covered Yarn is a type of yarn where a core yarn is twisted with a spandex filament yarn. The twist allows the spandex yarn to be securely wrapped around the core yarn.   2. Properties:    - ACY: Due to the presence of air bubbles, ACY tends to have a softer and bulkier texture with a lower elasticity compared to SCY. It offers good breathability and moisture management properties.    - SCY: SCY retains the inherent stretch and elasticity of the spandex filament yarn, providing excellent recovery and stretch properties to fabrics. It offers a firm and compact texture with higher elasticity compared to ACY.   3. Applications:    - ACY: Air Covered Yarn is commonly used in applications that require moderate stretch and improved comfort, such as athletic wear, lingerie, socks, and home textiles.    - SCY: Spandex Covered Yarn is primarily used when higher stretch and recovery properties are desired, making it suitable for sportswear, swimwear, waistbands, and medical fabrics.   In summary, the main difference between Air Covered Yarn (ACY) and Spandex Covered Yarn (SCY) lies in their construction method and resulting properties. ACY relies on air bubbles for coverage, providing a softer feel and lower elasticity, while SCY utilizes twisted spandex for enhanced stretch and recovery. The choice between the two depends on specific fabric requirements and desired performance characteristics in different textile applications.