Purify the air in your most sensitive environments. These filters remove 99.999% of dust and other particles, so they're best in areas where high air purity matters, such as semiconductor, pharmaceutical, and aerospace facilities. Constructed with fibers more densely woven than a HEPA filter, they catch 10 times more particles. However, they need to be changed more often than HEPA filters because they collect contaminants more quickly. All are UL rated for flame retardance.