Overview
ISO 18782:2023 - Textiles - Determination of dynamic hygroscopic heat generation specifies a laboratory test method to measure hygroscopic heat produced when air changes from low to high humidity on one side of a sheet-shaped textile. Applicable to all sheet-form textile materials, the standard quantifies the temperature rise (ΔT) caused by adsorption of water vapour on a textile surface and defines instruments, specimen preparation and test conditions for reproducible results.
Key topics and technical requirements
- Test principle: Instant switching from low-humidity to high-humidity air causes a transient temperature increase at the specimen surface; the peak temperature difference is recorded as ΔTmax.
- Controlled atmosphere: Measurements are made in a constant temperature and humidity chamber at 20 °C ± 2 °C. Low-humidity air is taken from chamber air at 40 % RH ± 3 % and a flow rate of 1.0 l/min ± 0.1 l/min.
- High-humidity generation: High-humidity air is produced by a bubbling bottle (water, grade 3 per ISO 3696) and typically reaches about 90 % RH ± 5 %; the high-humidity flow rate is set using a cotton control specimen so that its ΔTmax is 2.8 °C ± 0.3 °C.
- Apparatus: Multi-position testing rig (four measuring units) including specimen holder, polystyrene foam specimen table, film-type thermometer (accuracy ±1.2 %), flowmeters (±10 %), rectifying plate (perforated metal), humidity sensor and continuous monitoring recorder (≤1 s interval).
- Specimen preparation: Cut four 60 mm ± 2 mm square specimens per sample, dry in oven at 105 °C ± 3 °C for ≥3 h, cool in desiccant then condition in chamber for >12 h before testing.
- Supporting clauses and annexes: Clause details for calculation and test report, Annex A for airflow determination, Annex B interlaboratory results, Annex C example apparatus, Annex D interpretation guidance.
Applications and who uses this standard
- Textile R&D and product development: Evaluate and optimize warm-feel performance of natural and engineered fibres.
- Quality control laboratories: Routine testing for hygroscopic heat generation to ensure batch-to-batch consistency.
- Apparel and functional garment manufacturers: Inform thermal comfort claims, insulation system design, and material selection.
- Fiber producers and material scientists: Compare hygroscopic performance of natural vs. synthetic or treated fibres.
- Standards organizations and test houses: Use for comparative studies and harmonized reporting.
Related standards
- ISO 139 - Standard atmospheres for conditioning and testing
- ISO 3696 - Water for analytical laboratory use
- ISO 105‑F02 - Cotton adjacent fabric specification (control specimen)
Keywords: ISO 18782:2023, hygroscopic heat generation, textiles testing, dynamic hygroscopic heat, ΔTmax, bubbling bottle, film-type thermometer, textile thermal comfort.
