Oxygen No. represents the volume of reducing substances remained in feather & down material. This indicator is measured by the amount of oxygen that has been consumed by the reducing substance when oxidized under certain conditions. The unit of Oxygen No. is mg (oxygen)/ 100g (down).

Down’s chemical property is quite stable; it is hard to be oxygenated. The reducing substances inside has active chemical property, whether they are organic or inorganic. In some cases, such as humid environment, reducing substances will help microorganism increase and damage the feather & down quality. Reducing substances could be largely decreased after the proper washing process. Therefore, the Oxygen No. is a critical indicator in the down quality evaluation.