The filter is invisible nasal air purifier, filter into the nasal cavity, through the built-in filter, filter out particulate matter is not clean, to filter the air, with the filters people can always air fresh and clean. The product is compact and easy to carry. It is commonly known as "invisible mask". It does not affect the face-to-face communication and communication with other people. It also solves the problem that wearing masks does not breathe smoothly and has the characteristics of moisture for a long time.