Ugly Duckling's PM2.5 filter is a 5-layer activated carbon filter that can be inserted in the side pocket of the Ugly Duckling Face Masks to improve the filtering performance.
PM2. 5 refers to particles that have diameter less than 2.5 micrometres (more than 100 times thinner than a human hair) and remain suspended for longer. These particles are formed as a result of burning fuel and chemical reactions that take place in the atmosphere.
Filters can be effective for 1 to 3 days, which could amount to 1 to 2 weeks of occasional use. It is also stated that filters can be changed once every week, so a mask should be lasting you for a month or two, depending on the frequency of use.