Insulation performance testing, standard analysis and clothing selection

Author |Cao Yuansen

Unit |Chuangbiao (Beijing) Testing Technology Service

With the arrival of cold winter, people will buy some warm clothing to protect themselves from the cold. However, there are many kinds of warm clothing on the market, and the categories are diverse. When consumers purchase, they will encounter various confusions and do not know what kind of warm clothing. The thermal insulation effect is better. The following introduces the current status of testing of thermal insulation performance of clothing, test principles, influencing factors and related standards of thermal clothing, as well as key points for purchasing thermal clothing.

Current status of thermal insulation performance testing

At present, among the commonly used test method standards in China, the commonly used characterization indicators of thermal insulation performance include thermal resistance and thermal insulation rate. In domestic product standards, thermal insulation rate is usually used to evaluate the thermal performance of clothing. Thermal resistance generally only appears in method standards. Domestic clothing product standards rarely use thermal resistance value as an assessment indicator.

“GB/T 11048-2008 Determination of thermal resistance and moisture resistance of textiles under steady-state conditions” implemented in 2008 has replaced the old standard “GB/T 11048-1989 Test of thermal insulation performance of textiles”. Compared with GB/T 11048-1989, GB/T 11048-2008 adds thermal resistance indicators, Crow value and thermal conductivity indicators, and cancels the thermal insulation rate indicator in the old standard. Therefore, in the new standard, we can only get the test results of thermal resistance, but not the thermal insulation rate index. In the new standard, two types of instruments are used, type A instrument – evaporation hot plate method, and type B instrument – static plate method. Among them, type B instrument is the same as the instrument used in method A in GB/T 11048-1989. That is to say, method B in GB/T 11048-2008 is basically the same as the thermal insulation rate test method A in GB/T 11048-1989. The result obtained is the thermal resistance index, not the thermal insulation rate index.

Although the new version of the standard GB/T 11048-2008 has been released, the old standard GB/T 11048-1989 A method is still used as the test method in the product standards for thermal clothing. For example, “FZ/T 73022-2012 Knitted Thermal Underwear” uses the GB/T 11048-1989 A method as the test method for thermal insulation, and the thermal insulation rate as the assessment indicator. In this way, during the process of submitting products for inspection, customers will ask why they still need to use the old method standards for testing when there are already new testing method standards, which makes the inspection personnel full of confusion during the inspection process. Since the current product standards still use thermal insulation rate as the assessment indicator and do not use thermal resistance as the assessment indicator, the old standard GB/T 11048-1989 A method is still used as the test method in the current thermal clothing testing. It is recommended that it be used in the future. When formulating standards for thermal insulation products, thermal resistance is still used as the assessment indicator, and the new version of the standard GB/T 11048-2008 is used as the test method to avoid disagreements.

The definition and experimental principle of thermal insulation rate

Insulation rate: In the thermal insulation tester, the difference between the heat dissipation without the sample and the heat dissipation with the sample is the percentage of the heat dissipation without the sample.

Insulation rate = (Q1-Q2)/Q1×100%

Q1: Heat dissipation without sample

Q2: Heat dissipation when there is a sample

Experimental principle: Cover the sample on the test plate of the thermal insulation tester. The test plate, bottom plate and surrounding protective plates are all at the same temperature as the electric heat control, and the constant temperature is maintained by cutting off the power, so that the heat of the test plate can only By radiating in the direction of the sample, the heating time required for the test plate to maintain constant temperature within a certain period of time is measured, and the heat preservation rate of the sample is calculated.

The definition and experimental principle of thermal resistance

Thermal resistance: The ratio of the temperature difference on both sides of the sample to the heat flow per unit area passing vertically through the sample. Thermal resistance is measured in square meters Kelvin per watt (m2·K/W), which represents the dry heat flow through a specified area of the textile under stable temperature conditions.

Experimental principle: The sample is covered on the electric heating test plate. The test plate and the protective plates around and at the bottom can maintain the same constant temperature, so that the heat of the electric heating test plate can only be dissipated through the sample; the humidity-controlled air can be parallel to the test plate. After the experimental conditions reach a stable state, the heat flow through the sample is measured to calculate the thermal resistance of the sample.

Domestic relevant standards

Test method standards:

“GB/T 11048-1989 Thermal Insulation Performance Test of Textiles”

“GB/T 11048-2008 Determination of thermal resistance and moisture resistance of textiles under steady-state conditions for physiological comfort”

Product standards and indicators:

“FZ/T 73022-2012 Knitted Thermal Underwear”

Assessment indicators: insulation rate ≥ 30%,

Test method: GB/T 11048-1989 Method A

“FZ/T 73016-2013 Knitted thermal underwear sheet type”

Assessment indicators: insulation rate, excellent products ≥ 55%, first-class products, qualified products ≥ 45%,

Test method: GB/T 11048-1989 Method A

“FZ/T 64002-2011 Composite thermal insulation material metal-coated composite flakes”

Assessment indicators: Hot�(m2·K/W) low index ≥0.095

Test method: GB/T 11048

“FZT 64020-2011 Composite thermal insulation material chemical fiber composite flakes”

Assessment index: Thermal resistance (m2·K/W) low index ≥0.090
Test method: GB/T 11048-2008 Type A instrument

Factors affecting thermal insulation rate

1. Influence of the thermal conductivity of clothing materials. The thermal insulation rate of clothing mainly depends on the thermal conductivity of the fiber material. The thermal conductivity is used to measure the material’s ability to conduct heat. The smaller the thermal conductivity of the fiber, the better the thermal insulation. The thermal conductivity of wool and acrylic is lower than that of cotton and other chemical fibers. Therefore, the same clothes made of wool and acrylic have better thermal insulation than clothes made of other ingredients.

2. The influence of the bulkiness of the clothing structure. Improving the bulkiness of the clothing structure can increase the content of the still air layer in the clothing material. This can effectively isolate the human body from the cold air in the external environment, but only pursues the fluffiness of the clothing material. The thickness is not enough. A certain thickness is needed to ensure the absolute content of air. It is difficult for very thin materials to achieve high warmth retention. Generally speaking, fluffy and thick sweaters have better thermal insulation effects than other lightweight clothing.

Key points for purchasing warm clothing

1. You can choose some clothes with a fluffy fabric structure, a relatively large thickness, and a large amount of air layers. For example, fleece fabrics and fluffy fabrics have better warmth retention than ordinary fabrics, and down jackets and cotton clothing have better warmth retention than ordinary clothing.

2. Choose some clothing styles with shrinking designs, such as necklines, cuffs, hem openings and leg cuffs of pants. This shrinking design can ensure that there is no air layer between the body and the clothing. Flow occurs, thereby achieving the effect of keeping warm. It is recommended that you wear a scarf around your neck so as not to expose your neck. You can wear a long coat on your top, which can effectively protect your waist. You can wear high-top styles when wearing shoes and boots, which can protect your feet from being exposed.

3. When purchasing down clothing, you must consider the filler, down content, filling amount, and down fluffiness. Generally speaking, goose down has better warmth than duck down; the down content refers to the content of lobular down, and the down content of down jackets should not be too low; the down filling refers to the weight of all the down filled in a down jacket. A down jacket should be filled with enough down to ensure the warmth of the down jacket; fill power refers to the elasticity of the down jacket. When purchasing, you can squeeze the down jacket with your hands to see if the down jacket can return to its original shape. Try to buy some fluffier down jackets. ; By looking at the clothing tag, you can see the filling type, down content, and down filling amount of the down jacket. Combining these marked information, we can refer to the purchase of down jackets.

4. If the clothing you wear is often outdoors, the clothing should mainly be cold and windproof. You can choose some windproof clothing for the outer layer of clothing. The outer fabric of the garment should have low air permeability, be relatively tight and thick, and you can choose some coated fabrics. The clothes you choose can be windproof cotton clothes or jackets.