This can be purchased to refill your mask, but it is not mandatory to purchase, as each regular mask comes with 1 filter when you make your first purchase.
You can also purchase your filters elsewhere or use alternatives. Each filter can last approximately 1 - 3 days depending on usage. ( Please visit our care instructions page for more details on how to use filter properly ) ( Open Here )
Please ensure to wash your mask after every use and remove the filter when doing so.