The Thermal Manikin Evaporative Resistance Test defined by ASTM F2370 is a standardized procedure used to measure the evaporative resistance of clothing materials and ensembles. The test evaluates how well a garment allows the evaporation of moisture from the human body, which is a critical factor for thermal comfort and performance, especially in environments where sweat and heat dissipation are key to maintaining comfort. This test is particularly important for protective clothing, sportswear, military gear, and outdoor apparel designed for various environmental conditions.
Evaporative resistance is a measure of a material's ability to resist the passage of moisture (in the form of sweat) from the skin to the atmosphere. A higher evaporative resistance indicates that the material or garment inhibits the evaporation process, which could lead to increased body temperature and discomfort. On the other hand, low evaporative resistance means that the garment allows sweat to evaporate more easily, promoting cooling and comfort.
The evaporative resistance of clothing is a key factor in determining thermal comfort and heat stress. In high-heat environments, such as those encountered in industrial settings, military operations, or during intense physical activities, managing sweat evaporation is critical to preventing heat stress and maintaining performance.
The ASTM F2370 standard provides the methodology for measuring evaporative resistance using thermal manikins. This test uses a thermal manikin equipped with sensors to simulate the human body’s surface and measure the evaporative resistance of various clothing materials and combinations. The standard outlines the specific procedures and conditions under which the test should be conducted to ensure consistency and accuracy.
Thermal Manikin: The test uses a thermal manikin that is heated to simulate the heat of the human body. The manikin is designed to replicate the skin surface’s thermal properties, including temperature and moisture transfer characteristics.
Environmental Control: The test is performed under controlled environmental conditions, including air temperature, relative humidity, and air velocity. This helps ensure that the results reflect the garment's performance under realistic wear conditions.
Skin Temperature: The thermal manikin is maintained at a specific skin temperature to simulate human body heat under normal sweating conditions.
Evaporation Rate: The rate at which moisture evaporates from the manikin's surface is measured. This is directly linked to the evaporative resistance of the tested material or garment.
Air Velocity and Humidity: The airflow around the manikin and the humidity level are carefully controlled to simulate realistic environmental conditions. Changes in air velocity and humidity can significantly impact evaporative resistance.
Evaporative Resistance Formula: The evaporative resistance is calculated using the rate of moisture evaporation and the temperature of the manikin’s surface. The formula for calculating evaporative resistance (Ret) is typically:
Ret=(Tm−Ts)(m⋅A)Ret = \frac{(T_m - T_s)}{(m \cdot A)}Ret=(m⋅A)(Tm−Ts)
Where:
TmT_mTm is the temperature of the manikin's skin (in °C or °F),
TsT_sTs is the surrounding air temperature (in °C or °F),
mmm is the evaporation rate of sweat (measured in grams per minute),
AAA is the surface area of the manikin (usually in square meters or square feet).
This formula gives a value for the evaporative resistance in units of m²·Pa/W or cm²·Pa/W, depending on the standard measurement system used.
The test is generally performed under constant environmental conditions, but variations can be made to simulate different environments. The standard specifies the acceptable ranges for:
Air temperature (typically around 20°C to 30°C)
Relative humidity (typically between 20% and 80%)
Air velocity (typically 0.1 to 1.0 m/s)
The ASTM F2370 test is widely used in industries where clothing performance in various environmental conditions is critical. Some common applications include:
Military and Tactical Gear: For military personnel working in hot, humid environments, evaporative resistance is a crucial factor in ensuring comfort and preventing heat-related illnesses. The ASTM F2370 test ensures that military clothing and armor allow for adequate sweat evaporation, helping to maintain comfort during extended missions.
Firefighter Gear: Firefighters must endure extreme heat during emergencies. The ability of protective clothing to allow sweat evaporation is key to managing thermal stress during high-intensity situations.
Athletic Apparel: Clothing worn by athletes in hot or physically demanding conditions must allow sweat to evaporate to prevent overheating and maintain performance. The ASTM F2370 test helps designers optimize the breathability and moisture-wicking properties of sportswear.
Outdoor Apparel: Outdoor clothing designed for hikers, climbers, or workers in hot climates must be tested for evaporative resistance to ensure it supports cooling during physical exertion.
Workwear for Hot Environments: In industries such as construction, mining, and manufacturing, workers are often exposed to high temperatures. Garments must facilitate moisture evaporation to prevent heat stress. The ASTM F2370 test ensures that protective clothing allows for this necessary evaporative cooling.
Clothing Testing: Researchers and manufacturers use the ASTM F2370 standard to test new fabrics and materials, evaluating how they perform in terms of evaporative resistance. This helps develop better clothing for both everyday use and specialized applications.
Accurate and Repeatable Results: Thermal manikins provide precise, objective, and reproducible data on evaporative resistance, making the test highly reliable.
Real-World Simulation: By using a thermal manikin to simulate human heat transfer and sweat evaporation, the test closely mimics actual human performance under various environmental conditions.
Improved Product Design: The test provides valuable data to optimize clothing designs for thermal comfort, helping to develop garments that are better suited to their intended environments.
Regulatory Compliance: For industries that require compliance with health and safety regulations, such as protective clothing or military uniforms, ASTM F2370 provides a standardized, recognized test method to ensure garments meet required standards.
