Standard Atmosphere and Sample Conditioning
topic
All yarn testing must be performed after conditioning at standard atmosphere: 20±2°C, 65±2% RH (ISO 139). Conditioning time: minimum 24 hours for yarn packages, 4 hours for small samples. Unconditioned yarn has: lower moisture (higher static, higher apparent tenacity for hygroscopic fibres like cotton), different elongation, and different electrical capacitance (affecting Uster Tester readings). Pre-conditioning at 35°C, 10% RH for 1 hour before standard conditioning is required for polyester blends.
Role
Standard conditioning is the procedural foundation of reproducible test results. A 5% RH difference between laboratories can cause 3–5% difference in measured yarn tenacity for cotton — enough to pass or fail a contract specification. Understanding conditioning requirements is essential for comparing results between mills, resolving customer disputes about test data, and achieving ISO 17025 laboratory accreditation.