One style. Safety. Though our masks are non-medical grade forms of protection, the signature HOPE mask is designed so that you can insert our complementary PM2.5 activated carbon filters inside, or other accommodations on your own. One filter INCLUDED with purchase of mask. Three-layer technology The HOPE mask is compiled of three skin-friendly jersey layers, with viscose jersey elastic straps that adjust to your personal fit. It is designed for style, comfort, durability, and protection. PM2.5 Activated Carbon Filter The PM2.5 activated carbon filter utilizes five-layer technology to ensure efficient filtration from harmful airborne substances. PM2.5 filters are effective in blocking the greater majority of airborne particulates, even to the finest nanoparticles. The name “PM2.5” originates from their original use in protection against Particulate Matter 2.5, which is the smallest and most harmful form of air pollution. How long does one filter last? You can use one PM2.5 filter for up to 16-24 hours at a time, around 1-2 times a week. The filter never loses its effectiveness, thus one can be used for relatively long amounts of time before disposal. We recommend replacing your mask filter every month or so, depending on how vigorously it is being used. If you experience more difficulty breathing or find your filter becoming rather unsanitary, replace it accordingly. Do not wash for re-use. Size Small fits most young children (2-7 years) Size Medium fits most youth to young adults (7-adult) Size Large fits most adults Please see photo for exact mask dimensions