This snazzy and smart Filtering Mask with Math Pattern looks great while keeping you covered! The outer layer is made of a tightly woven cotton that holds its shape. The inner layer is made of a soft brushed cotton layer. The inner layer has an overlapping slot that you can slip a PM2.5 filter into. The mask comes with two filter pieces. https://elecena.pl/product/17502704/filtering-mask-with-math-pattern 2021-04-07 https://elecena.pl/product/17502704/filtering-mask-with-math-pattern 2023-05-12