There are a few fake active carbon masks which use fake active carbon pre-filter in the market.

For some active carbon masks, they are just "BLACK" masks, not active carbon masks. They might look like Active Carbon Masks because the appearance is BLACK, but the suppliers just die the color on the non-woven substrate which contains no charcoal particle. The genuine active carbon is carbonized under extreme high temperature. Therefore, the active carbon will not melt or disappear even undertaken high temperature afterwards. Just cut the active carbon mask to take out the active carbon pre-filter. Burn the active carbon pre-filter. If you can not find any remnant of charcoal particle or charcoal fiber, then you might purchase the fake active carbon mask.