Filter Efficiency

  • Filters used in surgical masks and respirators are considered “fibrous” in nature - constructed from flat, non-woven mats of fine fibers
  • Fiber diameter, porosity (the ratio of open space to fibers) and filter thickness all play a role in how well a filter collects particles (ie., type of material, 1 ply vs 3 ply)
  • There are 4 mechanisms by which filters work, 3 mechanical (primarily large particles) and 1 Electrostatic (large and small)
    • N95 respirators are usually manufactured with a melt blown thermoplastic layer
      sandwiched between multiple fibrous layers

(Source: CDC, others)

Sample specs from a Disposable Face Mask (can vary)

  • Inner Layer : Spun-bound polypropylene
  • Middle Layer: Melt-blown polypropylene
  • Outer Layer : Spun-bound polypropylene

Sample specs from a KN95 mask manufacturer (can vary)

  • Non-woven Polypropylene Isolation Layer
  • Melt blown Thermoplastic Layer (Electrostatic charged, usually PP)
  • Two-ply Heat Sealed Cotton
  • Cotton Comfort Layer