Diaper Air Permeability Testing

Diaper air permeability testing mainly conducts scientific testing and analysis on the air permeability rate determination, moisture vapour transmission rate testing, gas exchange resistance evaluation, thermal and moisture resistance testing, air permeability uniformity analysis, and microclimate temperature and humidity monitoring, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Air permeability rate determination: The air permeability rate is the core quantitative indicator for measuring the air permeability of the diaper, referring to the volume of air passing through the unit area of the specimen per unit time under the unit pressure difference. The test results are usually expressed in millimetres per second or cubic metres per square metre per second. This indicator directly reflects the ability of the diaper materials (especially the breathable film or nonwoven) to allow the air to pass through. The higher the value, the better the air permeability.

Moisture vapour transmission rate testing: The moisture vapour transmission rate is used to evaluate the ability of the diaper to allow the water vapour to pass through, simulating the process of the evaporation and discharge of the sweat and moisture from the baby's skin. The testing is usually carried out under the specific temperature and humidity conditions, measuring the mass of the water vapour passing through the unit area of the specimen per unit time, with the unit of g/(m²·24h). This testing is crucial for evaluating the "dryness" of the diaper and preventing the "diaper rash".

Gas exchange resistance evaluation: This testing evaluates the obstruction of the overall structure of the diaper (including the topsheet, absorbent core and backsheet) to the gas flow. By measuring the resistance or flow rate of the air passing through the complete sample under a certain pressure difference, the pros and cons of its air permeability can be comprehensively evaluated. The lower resistance means that the air circulates more easily, helping to maintain the air circulation of the micro-environment inside the diaper.

Thermal and moisture resistance testing: The thermal and moisture resistance is the comprehensive embodiment of the thermal resistance and moisture resistance, reflecting the degree of obstruction of the product to the heat and moisture transfer under the specific conditions. The testing uses the simulated skin (hot plate) in the specific temperature and humidity environment, measuring the energy required to maintain the constant temperature and humidity of the hot plate. The lower thermal and moisture resistance means that the product can discharge the heat and moisture faster, keeping the skin dry and comfortable.

Air permeability uniformity analysis: This item aims to detect whether there are significant differences in the air permeability of the different parts of the diaper (such as the front waist, back waist, crotch and leg cuffs). Through the multi-point sampling testing of each zone, the uniformity of its air permeability is evaluated. The uniform air permeability can avoid the local overheating or moisture accumulation, improving the overall use comfort.

Microclimate temperature and humidity monitoring: This is a dynamic simulation testing closer to the actual use scenarios. The diaper is worn on a mannequin simulating the baby's body posture, and after absorbing the simulated urine, the temperature and humidity change curves of the microclimate zone formed at the contact surface between the diaper and the "skin" are continuously monitored. This data can intuitively reflect the actual breathable and heat-dissipating effects of the product.

Testing Scope

Baby diapers/diaper pads: This is the most important application object of the air permeability testing, covering all the products of the different age groups (NB, S, M, L and XL), different styles (pants type and tape type) and different market positions (high-end and mass market). The testing needs to consider the influence of the structural differences of the different sizes on the air flow path, ensuring that all the products can meet the breathing needs of the delicate baby skin.

Adult incontinence care products: Including the adult diapers, care pads and pull-up pants. Due to the more sensitive skin of the user group, the possible long-term wearing, and usually the larger excretion volume, the requirements for their air permeability are more stringent. The testing needs to simulate the larger loads and longer wearing times, evaluating their persistent air permeability under the extreme conditions.

Diaper raw materials: The testing scope extends to the key materials constituting the diaper, such as the breathable backsheet films (PE breathable films), nonwoven topsheets and composite absorbent core materials. The pre-testing of the air permeability of the raw materials can control the quality of the finished products from the source, and provide the data support for the material selection and process optimization.

Pet urine pads and diapers: With the development of the pet care market, the comfort of the pet hygiene products has also attracted attention. The air permeability testing principle is similar to that of the human products, but the pressure points and evaluation standards need to be adjusted according to the body shapes, lying postures and behaviour characteristics of the pets (such as the cats and dogs).

Sanitary napkins and panty liners: Although the liquid types and skin contact environments are different from the diapers, the female hygiene products also have the high requirements for the air permeability, to avoid the stuffiness and bacterial growth. The testing focuses on the air and moisture vapour transmission performance changes in the presence of the simulated menstrual fluid, as well as the rapid rewet and drying ability of the topsheet materials.

Medical care pads and protective pads: The care pads used for the long-term bedridden patients have the dual high requirements for the air permeability and leakage resistance. The testing needs to evaluate whether the water vapour can effectively escape while bearing the larger liquid pressure (leakage resistance), to prevent the bedsores and skin infections.

Testing Methods

Air permeability tester method (pressure difference method): This is the most classic and commonly used method, mainly in accordance with the standards such as GB/T 5453 and ISO 9237. The specimen is clamped in the test head, a fixed pressure difference is formed on both sides of the specimen, and the air permeability rate is calculated by measuring the air flow passing vertically through the specimen within the specified time. This method has the mature equipment, accurate results and strong comparability, and is suitable for the air permeability evaluation of the films, nonwovens and light composite materials.

Moisture vapour transmission cup method (gravimetric method): Used to determine the moisture vapour transmission rate, following the standards such as GB/T 12704 and ASTM E96. The desiccant or water is placed in the moisture vapour transmission cup, the specimen is used to seal the mouth, and then it is placed in a constant temperature and humidity chamber. The mass change of the cup is regularly weighed, and the water vapour transmission amount per unit time and unit area is calculated. This method is simple to operate and can effectively simulate the moisture transmission under the static conditions.

Sweating guarded hotplate method (skin model method): This is an advanced testing method simulating the sweating state of the human skin, in accordance with the standards such as ISO 11092 and GB/T 11048. The hot plate of the instrument simulates the skin (maintaining the constant temperature and evaporating the water), the specimen is covered on it, and the evaporative heat dissipation and dry heat dissipation required to maintain the hot plate conditions are measured, thereby calculating the moisture vapour transmission index, moisture resistance and thermal resistance of the specimen. This method has the results close to the actual wearing experience.

Dynamic vapour transmission method: Different from the static moisture vapour transmission cup method, this method forms a stable humidity gradient on both sides of the specimen, and uses the sensors to directly and continuously measure the water vapour transmission rate, as described in the standard ASTM F2298. This method has the fast testing speed and high degree of automation, can monitor the moisture transmission process in real time, with more precise data.

Microclimate chamber simulation testing method: This is an integrated system testing method. The complete diaper product is placed in a microclimate chamber simulating the human body temperature and humidity, even combined with a liquid delivery system, and the changes of the multiple parameters such as the temperature, humidity and air pressure in the chamber are monitored in real time. This method can comprehensively evaluate the influence of the product design (such as the sealing of the waist and leg cuffs) on the overall air permeability from the system level.

Infrared thermography assisted analysis method: As a non-contact and visual auxiliary means, in the air permeability testing, an infrared thermal camera is used to monitor the temperature distribution changes of the sample surface after heating or loading the liquid. The areas with the uniform temperature and fast heat dissipation usually correspond to the better air permeability. This method can intuitively reveal the weak links of the air permeability.

Testing Standards

Domestic Standards:

1. GB/T 5453, Textiles — Determination of the permeability of fabrics to air

2. GB/T 12704, Textiles — Test method for water vapour transmission of fabrics

3. GB/T 11048, Textiles — Physiological effects — Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded-hotplate test)

International Standards:

1. ISO 9237, Textiles — Determination of the permeability of fabrics to air

2. ISO 11092, Textiles — Physiological effects — Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded-hotplate test)

3. ASTM E96, Standard test methods for water vapor transmission of materials

4. ASTM F2298, Standard test methods for water vapor diffusion resistance and air flow resistance of clothing materials

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Fabric air permeability tester: The core equipment, used to execute the pressure difference method testing. The main components include the test head, pressure difference sensor, flow meter, fan and control system. The high-precision instrument can provide the multiple optional test pressure differences, and automatically calculate and display the air permeability rate. To ensure the data accuracy, the instrument needs to be regularly calibrated with the standard orifice plates.

Constant temperature and humidity chamber: Provides the stable and standard environmental conditions (such as the temperature 23±1 ℃ and relative humidity 50±5%) for the moisture vapour transmission testing, material pre-treatment and thermal and moisture resistance testing. The temperature and humidity control precision and uniformity of the chamber are the key premises for ensuring the repeatability and comparability of the test results.

Sweating guarded hotplate instrument (skin model): With the precise structure, including a porous metal test plate (which can be heated and supplied with water for evaporation), a guard ring (to prevent the edge heat loss), a measurement control system and an environmental chamber. It is the equipment for measuring the "thermal and moisture comfort" indicators such as the thermal and moisture resistance, with the high price and high operation and maintenance requirements.

Dynamic water vapour transmission rate tester: The detection technologies such as the infrared sensors, electrolytic sensors or humidity sensors are adopted to directly measure the water vapour concentration or mass changes. The instrument is usually equipped with the multiple test chambers, which can test the multiple samples at the same time, and the data is automatically collected and processed by the computer software, with the high efficiency and small human errors.

Microclimate simulation testing system: This is a customized or semi-customized integrated equipment, which may include the hot plates/mannequins simulating the body postures, temperature and humidity sensor arrays, data collectors, automatic liquid delivery devices and environmental control chambers. It can reproduce the complex actual use scenarios and obtain the multi-dimensional performance data.

Infrared thermal camera: As an auxiliary observation equipment, its core is the infrared detector and optical imaging lens, which can convert the infrared radiation distribution of the object surface into the visual thermal images. In the air permeability research, it is used for the qualitative analysis of the "hot spots" and heat dissipation processes of the sample surface, providing the visual basis for optimizing the material structure and design.