The warmth-keeping performance of down has to start with the way of heat transfer. Generally speaking, heat is mainly transferred through conduction, convection and radiation. In the cold season, the body's heat is also dissipated to the surrounding colder space through these three methods. But in the case of wearing clothes or covering the quilt, the heat dissipation is mainly conduction. This requires low thermal conductivity of thermal insulation materials. Feather down has the characteristics of low thermal conductivity.
High-quality down has a higher bulkiness, which is unmatched by any other warm material. The more fluffy the warming material, the larger the gaps between the fibers of the material and the more stagnant air it contains. Air is a poor conductor of heat, which can prevent heat from being conducted to the surroundings. Therefore, the higher the bulkiness, the better the warmth retention performance. If you don't consider the difference in thermal conductivity between fabric fibers (in fact, the difference is very small), then down products have 20-50% lower thermal conductivity than ordinary fabrics of the same thickness, that is, warmth retention is 1-4 times higher. The higher the density of the product filler, the greater the thermal conductivity and the greater the heat loss. Down with high down content has a higher bulkiness, so that its product has a lower density under the same thickness, so it has higher warmth retention. Therefore, the use of down with a higher down content can appropriately reduce the weight of the filler, which can not only obtain the same warmth retention, but also reduce the weight of the product. This is the reason why down products have the characteristics of "light, soft and warm".
The higher the down content, the higher the bulkiness of the down, the better the relative warmth retention and the more comfortable it is. The down content of down is not 100%, unless it is selected by hand, the down content of machine sorting can reach up to 95%. Down filling material must contain a certain proportion of small hair pieces, because the hair pieces can play a role in rapid rebound. Therefore, determining the appropriate down content can reduce the amount of down filling and achieve the same purpose of keeping warm.