How clothing warmth is tested: hot plates, manikins and emittance
Clothing warmth is tested at three levels. Fabrics are measured on sweating guarded hotplates (ISO 11092) for thermal and vapor resistance. Complete outfits are measured on heated thermal manikins (ASTM F1291, ISO 15831), with results in clo. Heat-reflective surfaces are rated for emittance with instruments such as portable emissometers (ASTM C1371). Each test answers a different question.
Why are there different tests for clothing warmth?
Warmth depends on the material, how layers are combined and how the garment fits and moves on a body. No single lab measurement captures all of that. Standards bodies therefore split the problem into material tests, whole-ensemble tests and surface tests.
Knowing which test produced a number is the key to interpreting it. A fabric's thermal resistance, a garment's clo value and a lining's emittance are all legitimate figures, but they are not interchangeable.
| Test | What is tested | Main result |
|---|---|---|
| ISO 11092 sweating guarded hotplate | Fabrics and material layups | Thermal resistance (Rct) and water-vapor resistance (Ret) |
| ASTM F1291 heated manikin | Complete clothing ensembles | Insulation in clo or SI units |
| ISO 15831 thermal manikin | Complete clothing ensembles | Thermal insulation |
| ASTM F2370 sweating manikin | Complete clothing ensembles | Evaporative resistance |
| ASTM C1371 portable emissometer | Flat, opaque, conductive surfaces | Emittance near room temperature |
What is a sweating guarded hotplate?
A hotplate test places a fabric sample on a heated metal plate held at skin-like temperature, surrounded by a guard ring that stops heat escaping sideways. The power needed to keep the plate warm shows how strongly the fabric resists heat flow.
ISO 11092 measures two values: thermal resistance (Rct) and water-vapor resistance (Ret), the second by supplying water to a porous plate so it sweats. The method covers fabrics, films, coatings, foams, leather and multilayer assemblies, with practical limits of about 2 m²·K/W for thermal resistance and 700 m²·Pa/W for vapor resistance. The 2014 edition has been superseded by a 2026 edition.
How does a thermal manikin test work?
A thermal manikin is a full-size, human-shaped figure with heated body segments held at skin-like temperature. Dressed in the outfit under test, it stands in a climate chamber while instruments record the power each segment needs to stay warm. Less power means better insulation.
ASTM F1291 measures the resistance to dry heat transfer from a heated manikin to a relatively calm, cool environment and reports results in clo or SI units. It is a static test on a standing manikin; the effects of body position and movement are not addressed. ISO 15831 is the corresponding international standard for measuring clothing insulation on a thermal manikin.
Sweating manikins add moisture. ASTM F2370 uses a heated, sweating manikin to measure the evaporative resistance of whole ensembles, which shows how well outfits let sweat escape.
What do manikin results leave out?
Standard manikin tests are baselines. Walking, wind and posture change the air layers inside clothing, and ASTM notes that results apply to the specific ensemble under the specific conditions, particularly air movement.
Researchers continue to refine conditions. A 2025 study in the International Journal of Biometeorology recommended testing insulation with a 10 mm air layer and wind speeds of 0.5 to 1.3 m/s to better represent real wear. It also found that thickness measured with a standard high-pressure gauge (ASTM D1777) could differ by more than twofold from a low-pressure method for one sample, because the gauge squashes loft.
How is emittance of heat-reflective fabrics measured?
Reflective linings are judged by their thermal emittance: how much infrared they emit compared with a blackbody, which for opaque materials also tells you their reflectance. ASTM C1371 describes a comparative method using a portable differential thermopile emissometer, calibrated against reference standards of known emittance, with precision better than ±0.02 units.
The method has boundaries. It is intended for opaque, highly conductive materials near room temperature and excludes specimens that are transparent to infrared or have significant thermal resistance. An emittance value describes a surface, not the warmth of a finished garment, which also depends on insulation, fit and coverage.
Why can a garment feel different from its lab rating?
Lab tests hold conditions steady so that results are repeatable. Real wear is not steady. You sit, kneel, carry loads, sweat and walk into the wind, and each change compresses insulation, pumps air out of the microclimate or dampens fabric.
Personal factors matter too. Body size, activity level and how the garment fits your shape all change the air layers inside it. Use lab figures to compare products fairly, then judge fit and function in the conditions you actually face.
How should buyers read warmth test claims?
Ask which standard was used and whether the result is for a fabric, a layup or a full garment.
Compare clo values only when they come from the same method and conditions.
Treat emittance or reflectance figures as material properties, not whole-garment performance.
Look for vapor or evaporative resistance data if you will be active or sweating.
Remember that movement, wind and moisture reduce real-world insulation below static lab values.
Key takeaways
Fabrics are tested on sweating guarded hotplates, outfits on heated manikins and reflective surfaces with emissometers.
ASTM F1291 and ISO 15831 manikin tests report whole-ensemble insulation, usually in clo.
ISO 11092 reports both thermal resistance (Rct) and water-vapor resistance (Ret) for materials.
ASTM C1371 emittance results describe a surface, not a finished garment.
Standard tests are static baselines; movement and wind lower real insulation.
Frequently asked questions
What is a thermal manikin?
It is a human-shaped test figure with heated segments that simulate skin temperature. Labs dress it in clothing and measure the power needed to keep it warm, which reveals how well the outfit insulates.
What does Rct mean on a fabric spec?
Rct is thermal resistance measured on a sweating guarded hotplate under ISO 11092, in square meter kelvin per watt. Higher Rct means the material resists heat flow more.
What is Ret and why does it matter?
Ret is water-vapor resistance, also from ISO 11092. Lower Ret means sweat vapor passes through more easily, which matters for comfort during activity.
Are manikin tests done with movement?
The baseline ASTM F1291 test uses a standing, static manikin in calm air. Some labs run additional tests with walking manikins or wind, but those conditions must be reported to compare results.
Does a high reflectance rating mean a jacket is warmer?
Not by itself. Reflectance or emittance describes a material surface. Whole-garment warmth also depends on insulation, air gaps, fit, coverage and wind protection.
Related reading
Sources
ASTM F1291: Measuring the Thermal Insulation of Clothing Using a Heated Manikin, ASTM International
ASTM F2370: Measuring the Evaporative Resistance of Clothing Using a Sweating Manikin, ASTM International
ISO 11092: Textiles, Physiological effects, Measurement of thermal and water-vapour resistance (sweating guarded-hotplate test), International Organization for Standardization
ASTM C1371: Determination of Emittance of Materials Near Room Temperature Using Portable Emissometers, ASTM International
Comparative Analysis of the Thermal Insulation of Multi-Layer Thermal Inserts in a Protective Jacket, Materials (MDPI), via PubMed Central
Impact of garment construction and environmental factors on heat transfer, International Journal of Biometeorology (Springer Nature), 2025
About HEATJAC. HEATJAC is a thermal architecture company founded by an anesthesiologist. We design patented garment systems that capture, conduct and broaden warmth across the body, and we publish this knowledge hub because the science of staying warm should be public. HEATJAC products are not medical devices and are not intended to diagnose, treat, cure or prevent any disease.