Overview
ISO 20852:2020 specifies a laboratory test method to determine the total heat transfer through textile materials under simulated environments. The method evaluates the combined effects of dry heat transfer (conduction, convection, radiation) and evaporative heat transfer (latent heat due to moisture transport) using a guarded, transpiring hot plate. It applies to fabrics, films, coatings, foams, leathers and multilayer assemblies intended for use in hot environments or during high-activity conditions. The technique is limited by the apparatus capacity (for example, about 1 200 W/m2 for the maximum specifications referenced in ISO 11092).
Key Topics
- Principle: Total heat transfer Qt is obtained by combining measurements of dry heat and evaporative heat across a specimen evaluated on a transpiring hot plate.
- Measured resistances: The test derives thermal and evaporative resistance values, including total resistance of specimen plus air layer (Rct), intrinsic specimen resistance (Rcf), and evaporative resistances (A_R et, A_R ef), to characterise performance.
- Standardised gradients: The method uses defined temperature and vapour pressure gradients to separate dry and evaporative components (e.g., a 10 °C temperature gradient and a vapour pressure gradient referenced in the standard).
- Apparatus and materials:
- Guarded hot plate (transpiring plate) as described in ISO 11092.
- Analytical-grade water (ISO 3696) for wetting the plate when measuring evaporative resistance.
- A thin liquid barrier film (cellophane, 10–50 μm) to cover the porous plate where specified.
- Test conditions and sample preparation:
- Plate and guard temperatures typically maintained at 35 ± 0.5 °C; air temperature around 25 ± 0.5 °C.
- Air relative humidity and flow are controlled (example: 65 ± 4 % RH, air speed ≈ 1 m/s).
- Specimens are conditioned (e.g., 25 °C, 65 % RH for at least 12 h) and must fully cover the test plate without folds.
Applications
- Performance evaluation of cooling textiles, breathable membranes and protective garments intended for hot climates or high-exertion tasks.
- Product development and comparison of fabrics, coatings, foams and multilayer systems for thermal comfort and moisture management.
- Quality control and specification of materials used in sportswear, workwear, protective clothing and technical textiles.
Related Standards
- ISO 11092:2014 - Textiles - Measurement of thermal and water-vapour resistance using a guarded hot plate (basis for apparatus requirements).
- ISO 3696 - Laboratory water quality (used for evaporative resistance testing).
This summary focuses on practical value: ISO 20852:2020 provides a repeatable laboratory procedure to quantify how materials transfer combined dry and evaporative heat, enabling designers and specifiers to assess thermal comfort and cooling performance under controlled, standardised conditions.
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