Down vest The reason why down vest keeps warm lies in the characteristics of down material. Down comes from the breasts of ducks and geese. They are rich in fluff and air layers. These fluff can effectively isolate the cold air outside and prevent heat loss. At the same time, the air layer plays the role of heat preservation, so that heat is not easily lost. Therefore, the down vest can provide a good warm-keeping effect for the wearer. The warm-keeping effect of cotton vest is relatively poor, because although cotton has warm-keeping performance, its heat-insulating performance is different from that of down.