The secret of down jackets to keep warm can no longer be hidden

Produced by: Science Popularization China

Produced by: Xuelici (Dalian Institute of Chemical Physics, Chinese Academy of Sciences)

Producer: Computer Network Information Center, Chinese Academy of Sciences

In early November, affected by cold air, the temperature in many parts of the country dropped sharply. Two weeks later, strong cold air came again with a drop in temperature. In addition to relying on righteousness, down jackets should be one of the most practical tools for keeping warm.

Compared with other winter clothes, down jackets are light and thin, and have a better warmth-keeping effect. Why can thin and light down jackets keep you warm? Will thicker and longer down jackets keep you warmer? How to choose a down jacket scientifically?

Image source: Photographed by the author

Why is a thin down jacket so warm?

The metabolism in the human body continuously generates heat, and the body needs to dissipate the excess heat into the surrounding environment in order to maintain homeostasis.

There are three ways of heat transfer: thermal radiation, thermal conduction and thermal convection. Thermal conduction is the transfer of heat from a high-temperature object to a low-temperature object. Among gases, solids and liquids, the thermal conductivity of gases is the lowest. Therefore, relatively speaking, air can insulate and prevent heat loss.

Image source: Google

The ambient temperature is lower in winter. Due to air convection, the layer of air close to the body absorbs the body's heat, becomes lighter and increases in density. The vacant space will be filled in time by the cold air next to it, so we feel unbearable cold.

This requires wearing clothes to keep warm. There are many types of thermal insulation materials, which can be divided into natural thermal insulation materials such as animal fibers and plant fibers, synthetic thermal insulation materials such as polyester, acrylic, polypropylene and other synthetic fibers, and mixed thermal insulation materials. If a fiber can fix a large amount of still air and reduce the convection of air, it can have a good warming effect.

Down is just such an animal fiber. And in terms of warmth retention, there is no other thermal insulation material in the world that can surpass down. This is due to the special structure of down - the spherical fiber structure. Each down fiber is made up of many scales stacked together, and each scale is hollow. In these tiny pores, a large amount of still air can be fixed.

Scanning electron microscope photo of duck down (Source: Reference 1)

When you put on a down jacket, the down can absorb the body's heat and form an air insulation layer. The more air the insulation layer fixes, the better the warmth retention performance. In addition, the outer fabric of the down jacket can isolate the outer cold air, which can more effectively reduce the convection exchange between the air layer of the down and the outside air.

The warmth-keeping ability of a down jacket is mainly reflected in how much air the down can store after it becomes fluffy and the ability of the surface layer to isolate cold air.

There are five indicators that determine the thermal performance of down jackets: filling, down content, filling amount, fluffiness and fabric.

The "five major indicators" for selecting down jackets

Indicator 1: Filling

The filling refers to the type of animal down that is in the down jacket. Currently, goose or duck down is commonly used as the filling material for down jackets on the market. Down is very soft and elastic. Down only accounts for 8-10% of the feathers of a goose or duck. It grows under the feather roots, close to the abdomen and muscles between the wing sockets.

Image source: veer gallery

Down is further divided into: white goose down, grey goose down, white duck down and grey duck down. In most cases, goose down has larger down clusters and longer down fibers than duck down, and its warmth retention effect is slightly better, but this is not absolutely true. For most people, the warmth retention of duck down is sufficient. At the same time, goose down has much less odor than duck down, because ducks are omnivores and their down has a high fat content, while geese are herbivores and their odor is relatively mild. In terms of price, goose down has less output than duck down, so goose down is more expensive than duck down. For different colors of the same down, the thermal insulation effect and comfort are actually the same. White can be widely used for light-colored fabrics and is not transparent.

Down comparison chart (Image source: Reference 1)

Indicator 2: Down content

Down is made up of feathers and down, and it is the down that is mainly responsible for keeping warm. Down content refers to the percentage of down in the total filling of a down jacket. If the down content of a down jacket is 90%, it means that the down accounts for 90% of the filling, and the remaining 10% is feathers. According to national regulations, a down jacket can only be called a down jacket if the down content reaches 50% or more. Different down contents have different touches. For down jackets of the same size, the higher the down content, the better the warmth retention effect.

Feather (Photo source: veer gallery)

Rong Duo (Photo source: veer Gallery)

Indicator 3: Filling volume

Are you confused about the filling amount and the down content? Compared with the down content (ratio of down content) mentioned above, the filling amount refers to the weight of all the down filled in a down jacket. This is also a parameter indicator that should not be underestimated, because even if a down jacket has a high down content, but the filling amount is small, it will also affect the warmth effect. However, when choosing, you cannot just look at the weight, but also consider the total area of ​​a down jacket. Under the same filling amount, the warmth retention of a short down jacket and a knee-length down jacket will certainly be different.

Image source: Photographed by the author

Indicator 4: Fluffiness

Fill power, or FP, is an important indicator of the air storage capacity of down. It refers to the volume cubic inches occupied by one ounce (30 grams) of down under certain conditions. For example, if one ounce of down occupies 800 cubic inches, the fill power of the down is 800.

The fluffiness of down jackets on the market is generally divided into 550, 600, 700, 800 and 900, and the higher the price, the more expensive it is. Under the same premise, the higher the fluffiness of a down jacket, the more insulating air the down contains, so the thermal insulation performance will be better, and it will naturally be warmer. When choosing a down jacket, if the fluffiness is not indicated on the tag, you can relax and flatten the down product, let it recover naturally for three minutes, then press the product with your hand, and then release your hand. If it can quickly rebound and return to its original state, it means that the fluffiness of the down jacket is relatively good.

Image source: Photographed by the author

Indicator 5: Fabric

We all know that once a down jacket gets wet, it will shrink into a ball, and its fluffiness will be greatly reduced, and its thermal insulation performance will also be greatly reduced. This is also the biggest disadvantage of down compared to other thermal insulation materials, so the choice of down jacket fabric is also particularly important. Down jackets with poor anti-down performance or sewing needle holes that are too large will become thinner as they are worn.

Down jacket fabrics are updated very quickly. It has become a mainstream trend for outer fabrics to have anti-wrinkle, windproof, waterproof and other functions. For example, PTFE fabrics have extremely strong waterproof, snowproof, moisturizing, breathable, moisture-conducting and other properties; pure cotton PU coatings are smooth, delicate, tight, breathable, and easy to absorb sweat. At present, some brands of down jackets use silver-white anti-radiation materials on the inner fabrics to reduce radiation heat transfer, which further improves the warmth performance.

Image source: veer gallery

After talking about the tips for choosing down jackets, let’s take a look at the maintenance techniques for down jackets.

A good quality down jacket should not be washed too many times without affecting its cleanness. Frequent washing will damage the fiber protein structure of the down, making the down hard and brittle, affecting its warmth retention. It will also cause certain wear on the fabric and increase the possibility of hair formation.

If you want to wash your down jacket, you can choose dry cleaning or water washing according to the down jacket washing label. If you wash it with water, try not to use a washing machine. It is best to wash it by hand and rub it clean. After washing, do not wring it directly. You should squeeze out the water gently and then lay it flat or hang it up to dry. At the same time, after washing, pat the clothes to restore their fluffyness. The force should also be as gentle as possible to reduce damage to the down and extend its service life.

When you are walking in the howling cold wind, wrapping yourself in a down jacket and feeling warm is also a kind of happiness.

References

[1] Huang Chen. Comparative analysis of the performance of three types of down fibers[J]. Wool Textile Technology, 2021, 49(07), 85-89.

[2] He Yu. Testing and evaluation of warmth retention of down jackets[D]. Donghua University, 2020.

[3] Chen De. Research on thermal insulation mechanism and performance of different thermal insulation materials[D]. Beijing: Beijing Institute of Fashion Technology, 2019.

[4] Cui Peng. Detection mechanism and application of thermal insulation properties of high-loft fiber assemblies[D]. Donghua University, 2011.

[5] Quality comparison and selection of lightweight down jackets[J]. Textile Testing and Standards, 2019, 5(02): 31.

[6] Huang Cuirong, Yu Weidong, Xu Haiye. Study on the warmth retention of down jackets[J]. Journal of Wuhan University of Science and Technology, 2007, 4(01):25-29.