Filter Inserts Impact Cloth Mask Performance against Nano- to Micro-Sized Particles

Area of Science:

• Materials Science
• Public Health
• Fluid Dynamics

Background:

• Cloth face coverings are recognized by the CDC and WHO for slowing respiratory disease transmission.
• Adding high-filtration inserts to masks may enhance personal protection, but data on optimal coverage are limited.

Purpose of the Study:

• To investigate the impact of insert material and coverage on mask filtration efficiency, breathability, and overall performance.
• To determine the relationship between insert area ratio (IAR), filtration efficiency (FE), differential pressure (ΔP), and quality factor (QF).

Main Methods:

• Evaluated two fabrics (rayon, cotton flannel) with three insert materials (HEPA vacuum bag, sterilization wrap, coffee filter).
• Quantified FE, ΔP, and QF based on varying IAR.
• Used flow visualization to qualitatively assess particle flow and leakage during simulated exhalation.

Main Results:

• A complex trade-off exists between filtration during inhalation and leakage during exhalation.
• Increased IAR and insert filtration efficiency generally improved FE and ΔP, but the rate depended on insert type.
• Higher insert QF and near-complete IAR (close to 1) were necessary for significant performance gains, while increased ΔP led to more exhalation leakage.

Conclusions:

• Achieving effective source control requires minimizing exhalation leakage, necessitating low ΔP.
• Near-complete insert coverage (IAR close to 1) is critical to avoid performance degradation.
• The effectiveness of filtration inserts depends on a complex interplay of material properties, coverage, and breathability.