What’s the Best Filter for Homemade Masks in Healthcare Settings?

The coronavirus pandemic has triggered an unprecedented shortage of essential N95 respirators—leading many healthcare professionals to make and use their own masks. But many of the filter materials used in these homemade masks do not meet industry standards for protection in high-risk healthcare settings, reports a study in the October Journal of Occupational and Environmental Medicine.

Using the industry-standard testing system, the researchers compared six materials commonly used by healthcare workers for “do-it-yourself” masks. The study was led by Ian F. Jones, MD, of Madigan Army Medical Center, Tacoma, Wash.

Three of the improvised filter materials were effective in blocking very fine (0.3 microns) aerosol particles: true high-efficiency particulate air (HEPA) filters; fiberglass-free minimum efficiency reporting value 13 and 14 heating, ventilation, and air conditioning (HVAC) filters; and laboratory-grade polytetrafluroethylene (PTFE) filter paper. However, the PTFE material had high airflow resistance, which would lead to uncomfortable breathing conditions if used in a mask.

The other three materials tested—surgical sterilization wrap, disposable shop towels, and “HEPA-type” filters—did not effectively filter out fine aerosols. “[N]ot all ‘HEPA’ grade filters are created equal,” Dr. Jones and coauthors researchers write. Products labeled ‘HEPA-type’ or ‘HEPA-like’ may fail to meet standards for filtration efficiency.

Although the tested HVAC filters performed well, the researchers note that some of these products may contain fiberglass or potentially hazardous materials. With all materials, additional layers may improve the ability to filter larger particles, but not necessarily aerosols.

The study not only has implications for choosing filter materials, but also highlights the need for proper evaluation of improvised PPE at a time of continued shortages, Dr. Jones and colleagues believe. They conclude: “Further testing and regulation of specific mask designs is necessary prior to the widespread adoption of community-created masks in healthcare settings.”
About the Author
Dr. Jones may be contacted for interviews at ian.f.jones.mil@mail.mil.
ACOEM (www.acoem.org), an international society of 4,000 occupational physicians and other health care professionals, provides leadership to promote optimal health and safety of workers, workplaces, and environments.
About the Journal of Occupational and Environmental Medicine
The Journal of Occupational and Environmental Medicine (www.joem.org) is the official journal of the American College of Occupational and Environmental Medicine. Edited to serve as a guide for physicians, nurses, and researchers, the clinically oriented research articles are an excellent source for new ideas, concepts, techniques, and procedures that can be readily applied in the industrial or commercial employment setting.


Jones, Ian F. MD; Lammers DT, Conner JR, et al. Quality assurance during a global pandemic: an evaluation of improvised filter materials for healthcare workers. J Occup Environ Med. 2020;62(10):781-782.