Aspen Air Filter Overview

The Science Behind Our Filters

* The design standards used as references for material selection and mask design were ASTM F2100 2019 and the related standards.  

A note on terminology: Viruses are not living organisms; they must enter a living cell to multiply. Therefore, antiviral agents are said to “inactivate” viruses, not “kill” them.”

What are the filter materials?

All our filter layers are made of nonwoven polypropylene – also known as polypropene, a white, mechanically-rugged thermoplastic polymer that is partially crystalline and non-polar, lending it high chemical resistance. Two primary types of manufacturing methods produce filters with different fiber sizes, overlays, and properties:

  • Spunbond nonwoven polypropylene (SB): This layer is hydrophobic, and prevents fluid transfer through the maskfrom the outside, and the expulsion of droplets from the inside. This layer primarily works by the mechanical filter methods of inertial impaction and interception.
  • Melt blown nonwoven polypropylene (MB): This layer is manufactured specially to produce ultra-fine micro- and nanofibers in random orientations, and includes an additive that causes the fibers to hold a negative charge, such that it operates by both diffusion and electrostatic attraction, plus mechanically filtering very small particles. 

Methods of Face Mask Filtration

  1. Inertial Impaction: Particles with high inertia due to size or mass cannot follow the airstream as it is diverted around the filter fibers, and get stuck upon impact. This mechanism primarily collects larger particles.
  2. Interception: As airborne particles pass close to a fiber, they may be directly intercepted by the fiber. This mechanism primarily collects larger particles.
  3. Diffusion: Very small particles bounce around within the airstream as they are bombarded by air molecules, which causes them to deviate from the primary airstream and come into contact with a filter fiber. This mechanism primarily collects smaller particles.
  4. Electrostatic attraction/repulsion: Fibers treated to hold a charge will attract or repulse airborne particles that are also charged into other filter fibers. This collection mechanism works well on a wide variety of particle sizes.