Coronavirus / Covid-19 (SARS CoV-2, if you really care) can be transmitted through airborne particles. When out of your home, you should wear a quality mask. I believe these instructions should readily enable you to make one, and I believe it should be as high-quality a mask as one can make that is not an official N95 mask like those medical personnel use.

HUGE QUALIFIER: I am not a doctor, and while this is based on thorough research, I could nonetheless be wrong. I cannot be absolutely certain that the material I suggest, or the design I suggest, or the necessary fit that is required, can be truly as good as a commercially-manufactured mask. I have a proper 3M N95 mask, and to my best guess, the MERV 13 material I propose is very similar but not identical.

But, as we've seen, N95 masks are in short supply for the medical personnel who need them (some use improvised masks). I believe this is the best mask one can make. I encourage others to improve on the design.

Viruses are small particles, and the coronavirus is about 0.1 microns (1 ten-millionths of a meter): but this is not the figure to focus on -- it is the droplet it travels in. They are typically spread through an infected person sneezing, coughing, or breathing, which puts the virus particles in small water droplets into the air. The droplets can be relatively large and captured in even a cotton cloth, or they can be small and float about in the air for hours.

This story serves as a prime example: Note that the article refers to known incidence of viral airborne transmission. Ultimately, look at the countries that have low transmission -- notably, the Asian countries requiring masks.

Research demonstrates the following regarding exhaled particle sizes:

  • talking - 81 microns
  • coughing - 26 microns
  • breathing: - 1-4 microns

Research demonstrates the following regarding exhaled particles time in air:

  • talking: 6% still airborne after 30 minutes
  • coughing: 49% still airborne after 30 minutes
  • breathing: several hours

Any non-woven material is good -- yes, literally anything -- but preferably non-woven materials such as paper towels. The best material for trapping all sizes of particles is called "meltblown fiber," which are small polymer fibers randomly distributed in a sheet. Medical-grade masks (more accurately, "respirators") use this material.

Commercially-sold masks have a rating of (and are known as) "N95," meaning that they block at least 95% of all particles (far superior to surgical masks), and often block better than 95%. Unfortunately, at present there is a severe shortage of such masks due to an abject failure of government planning. Fortunately, the materials necessary to make an excellent high-quality mask are readily-available (at the end of these instructions I've provided additional information and links regarding filtration materials).

These are instructions on how make such a mask.


1. MERV 13 Home Heater Filter

Hardware stores and other such providers carry the highest-level conventional home heater filter. These "MERV 13" (or higher-rated) filters use similar types of fiber sheets as N95 masks, are tested to confirm they can block some particles such as viruses down to .3 microns, they must last for months with large volumes of air flowing through them, they are electrostatically treated to "collect" particles, and they are mold-resistant and therefore should be able to stand up to the wearer's respiration without a problem. And, they have a mesh support that allows them to be molded to the contours of each wearer's face.

* This mask is simple, and these filters still seem available. Even better would be to sandwich a sheet of good meltblown material between the filter material. However, I don't think it would be easy to locate, as good meltblown material is now pretty much being used exclusively by medical centers (hence the advice to make this mask from MERV 13 filter).

2. Foam Insulation Tape

Using foam insulation material both covers the mesh's sharp edges and also provides a soft compliant seal around the wearer's face. I used a "Camper Seal" foam tape that is 1-1/4" wide, 3/16" thick, and has an adhesive backing. It seems well-suited to this purpose, but there are probably other types that might work as well.

3. String/Elastic Bands

The mask can be held in place with string or elastic bands.

Step 1: Remove Filter From Its Cardboard Support

The filter needs to be removed from its cardboard support. Do so gently, as the cardboard is glued to the filter. It must to be removed without tearing the filter material.

Step 2: Flatten, Cut, and Fold a Section of Material to Make a Mask

Flatten, cut, and fold.

Flatten the filter material, which has pleats in it when used as a heater filter.

Cut to size: I have been using about a 8" x 12" section of material. I do not know if this is the best size, and perhaps another size would work better. (Unfortunately, I don't know how to cut a pattern to make a conical mask.)

Fold it over against itself, putting the mesh on the outsides, about 8" x 6." The filter's airflow direction doesn't matter, because, now that it is folded, air will now go through each side of the material. Trim it so that, as best as possible, the mesh sections are intact and there are no mesh wires poking out.

Step 3: Insulated Mask Rectangle

Cut the insulation. The insulation I used is a little over an inch wide, which helps when folding it over the edges of the material, and provides enough purchase to enable it to be stapled together.

Fold it over all four mesh edges (adhesive-side in). Squeeze the insulation flat, and staple the insulation sides together through the material. Leave gaps in your stapling in the middle of each of the four sides, as these points will later be pinched together to enable the mask to be snugly fit to the wearer's face.

Step 4: Put String Ties or Elastic Band on the Mask

I cut plain cotton twine into four 16-inch lengths. Elastic bands may work better. The staples' smooth sides will be the inside of the mask.

I used an opened paper clip to poke small holes at the corners (inside a mesh square if possible) between the insulation pieces. Taping the end of the string to the end of the paperclip, push the paperclip and string through the small hole. Tie the string or elastic and trim off the excess.

Step 5: Forming the Mask to the Wearer's Face (part 1)

Pinch the middle of the sides of the mask tightly together. Staple the pinched insulation, as close as possible to the base, to hold that pinch. The size of the pinch will vary with the size of the wearer's face.

Begin molding the mask to your face, bending and pinching the mesh. Pinch it in on the middle of the top and bottom sides to conform to the wearer's nose, and at the chin. The object is to make a large cone in the middle of the mask, and have it fit snugly all the way around where it meets the face: the mesh is strong, and will hold the shape you give it.

Step 6: Forming the Mask to the Wearer's Face (part 2)

Again, the object is to make a large cone in the middle of the mask, and have it fit snugly all the way around where it meets the face: the mesh is strong, and will hold the shape you give it. Tie the mask on and make additional adjustments. The insulation makes it very comfortable, so it can be tied fairly firmly.

Step 7: Your Mask Should Last -- But Don't Touch It

This mask is should be at least a bit more effective than MERV 13 air filtration because the material is folded double. Because this material is intended for home air filtration, it should last a long time. But of course, don't contaminate it or yourself by touching the filter material when you have been in a potentially contaminated space -- which is to say, everywhere you'll be wearing it.

Here is additional information about air filter materials:

This is the webpage content regarding this MERV13 product:

"Traps and blocks 98% of airborne particles... This pleated filter utilizes an electrostatic charge to remove very fine particles from your air, as well as potential allergens like mold, pet dander, bacteria — even particles that carry viruses... Our MERV 13 filters trap 98% of airborne particles as small as .3 microns... MERV 13 filters are comparable to MPR 1500/1900 and FPR 10."

You can review the helpful table on this webpage:

Here is the wiki page for MERV (including MERV 13) information:

For the final word, I'll go to the organization that established the rating system. Responding to the Covid-19 pandemic, they set out a complete and detailed analysis of how those in their industry should respond. And they advised installing MERV 13 (or higher) filters.


Step 8: