Make an n95 Equivalent Mask at Home

How to use commercially available materials to create a respiration mask equivalent to an n95 mask



Copyright

Copyright 2020, Ramon Glyde, All rights reserved

All trademarks and brand names mentioned herein are the property of the respective owners. All images were taken from publicly available products and free online sources. The author makes not copyright claim to the images herein reproduced.

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Disclaimer

The content of this work if for informational purposes only. The author makes not guarantees, written or otherwise, with regard to the performance of any mask or filter media described herein. The author makes no guarantees as to the efficiency or efficacy or your homebuilt mask. There are many factors that will make your mask better or worse depending on your particular abilities and the materials available to you.

(The FTC wants me to remind you that this website contains affiliate links. That means if you make a purchase from a link you click on, I might receive a small commission. This does not increase the price you’ll pay for that item nor does it decrease the awesomeness of the item.)



Table of Contents

Introduction

Materials

Method

Filter Capability Calculations

Breathability

FPR filters (Home Depot)

Filter Bypass



Introduction

It is becoming increasingly harder to find n95 masks at retail outlets due to the high demand caused by the corona virus. This book will show you how to make a similar such mask for use in dusty work environments.

(CAUTION: The materials described here were tested by the maker but NOT under the conditions required for official n95 designation. Use good judgment when evaluating the information here.)

The n95 masks that can be found are currently going for $6 dollars each in my area. In addition to issues with disease that are currently on many minds, these masks are needed for workspaces with fine dust particulate. The ability to make such masks for a dollar or less each is therefore greatly needed.



Materials

Here is what you will need:

Home heating/AC air filter rated MPR 2500 or MPR 2800 (preferred), MERV 14 (also preferred) MPR 1900, or FPR 12. I will explain the differences and reasons for preferring the 2500/2800 later. You can purchase these at the following links:

Good cutting shears or heavy scissors

Some kind of formable wire with rubber/plastic coating (available at home centers and auto parts stores) These can be purchased at:

Sometimes these formable wires are difficult to find. As an alternative, purchase a length of vacuum hose from an auto parts store and thread a strong, bendable wire through it.

Strong rubber bands or other elastic materials are needed to strap the mask to your face. These can be obtained at a hobby or fabric store as desired.



Method

Let’s get started.

Use cutting shears or strong scissors to cut out a rectangular piece of the filter material approximately 6” by 6” (You can tailor this size to your face later, cutting triangles and matching to your face size will greatly increase the number of masks you can cut from a single air filter).

STOP!! Filter media is directional. The direction of airflow matters in particulate capture. Be sure to label the material so you do not forget which side is front and which side is back. You want to suck air through the mask in the same direction as the heating/HVAC system would pull the airflow.

Due to the pleating of the materials this will result in a very long piece of filter media that is 6” wide. Flatten the material and cut out 6” by 6” rectangles (again be sure to label all pieces so you know intended airflow direction).

Separately, take a piece of formable wire and mold it to fit your nose and face as shown below.

Next, attach rubber bands or elastic material to the formable wire as shown in the next image in order to create a strap that will hold the formable wire frame firmly over your mouth and nose. There should be 2 attachment points on both sides. One just under where the nose bend happens and one at the jaw line. Adjust the locations as needed to get the best fit for you. Everyone is a little different.

Finally, layer 2 filter squares on each other and place into the wire frame as shown.

One great feature of these masks is the ability to form fit the bendy wire to any unique facial fit. Experiment a bit until you feel no bypass air coming from anywhere around the frame. Wet your face a little around the frame and see if you feel any cold spots where air is coming in around the mask. This is one of the most important issues as any bypass represents unfiltered air.

Now, layer the materials for the desired filtering level according to the Filter Capability Calculations in the next section. Be sure to face each rectangle (triangle if you are cutting for maximum filter media usage) in the same direction (airflow direction facing in). After this practical section there is a description of filtering efficiencies and why they may actually understate the capabilities shown here.

Trim and adjust the filter media as necessary for comfort and visibility (and fashion if you think it doesn’t look good enough – hat tip to daughters and wife) but DO NOT trim into the wire frame area. This would result in direct bypass of unfiltered air.

Although these are one-time use masks the wire and strap can be cleaned and reused. Therefore only the filter media needs to be discarded after use. Depending on the size of filter purchased, a single air filter can make anywhere from 30 to 50 double layer masks thereby cutting the cost of each mask to under a dollar.

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Filter Capability Calculations

Filter ratings and removal rates

Remember the filter media we are using was rated for use in HVAC and central heating systems. This is actually a good thing since the removal rates for particulate are tested using much higher airflow rates than human respiration (breathing). There is therefore a good chance that these rates understate the actual removal rates a mask made of these materials will achieve. Unfortunately the materials have not been tested or rated for use in masks/respirators and we are therefore unable to guarantee the values shown.

Let’s look at capture rates. According to the maker of Filtrete filters, filter testing for MPR ratings divides capture rates into particle size ranges as shown below.

E1 refers to capture rate for 0.3 to 1.0 micron particles

E2 refers to capture rate for 1.0 to 3.0 micron particles

E3 refers to capture rate for 3.0 to 10.0 micron particles

Due to the very small size of viruses and particulate we want to focus on the E1 capture rate. An officially tested n95 mask is rated to block greater than 95% of particles that are 0.3 microns in size or greater.

According to the maker, a Filtrete filter with an MPR of 2500 will capture 77% of E1 particles, 93% of E2 particles, and 97% of E3 particles. Using this as our mask filter media may not seem so good but, watch what happens when we layer 2 of these filter media on top of each other. For simplicity we will focus on the E1 particle capture rate.

The first layer will remove 77% or more of the particles down to 0.3 microns. This will leave 23% that will pass through. The second layer will remove 77% of the particles that passed through. That is 17.71% (.77 X 23%). When added to the original 77% that was removed, this means that 94.71% of the original particulate reaching the filter media was captured. The math is shown below.

77% removed by first filter layer

Of the remaining 23%, 77% removed by second filter layer (17.71%)

77% + 17.71% = total of 94.71% removal

This puts our homemade mask on par with an n95 mask.

The math for an MPR 2800 filter works out as follows:

81% removed by first filter layer

Of the remaining 19%, 81% removed by the second filter (15.39%)

81% + 15.39% = total of 96.39% removal

These numbers are why I recommend at least the 2500 air filter. The 2500 is available at most home centers. A 2800 filter will be even better but these are not always available locally (can be ordered online of course). These filters can be purchased at the links below.

Let’s consider the MPR 1900 filter.

62% removed by first filter layer

Of the remaining 38%, 62% removed by the second filter (23.56%)

62% + 23.56% = total of 85.56% removal (Not bad but considerably below the MPR 2500 and MPR 2800).

If a third layer is added we get an additional 62% of the remaining 14.44% removed (8.95%).

Therefore: 85.56% + 8.95% is 94.51%

Although this gets us to our goal, is adds considerable labor to the act of breathing.

The table below summarizes the particulate blocking abilities for various MPR ratings relative to the 0.3 to 1.0 micron level.

0.3 to 1.0 micron (E1) 0.3 to 1.0 micron (E1) 0.3 to 1.0 micron (E1) Removal rate (1 layer) Removal rate (2 layer) Removal rate (3 layer) MPR1900 62% 85.56% 94.51% MPR2200 69% 90.39% 97.02% MPR2500 77% 94.71% 98.78% MPR2800 81% 96.39% 99.38%





MERV ratings are shown below. You can see that a MERV 14 is approximately equivalent to an MPR of 2500. These filters are also readily available.

MERV ratings and capture rates.

Breathability

I have tested the 2 layer mask and found it slightly more difficult to pull air than the official n95 mask. It was sufficiently comfortable however to wear and breath for many hours of work.

The 3 layer mask was, however, more difficult and the wearer would be fatigued after an hour or more of usage. If this is all you need to go out and shop or do work in a dusty environment, than it is a viable alternative if better filter media is not available.

Improving Breathability

Commercially available masks have an integrated one-way valve that allows you to breath out easier. You can purchase a suitable one-way valve (called a check valve) at the link below.

Simply cut a hole or slit into the filter media and integrate the check valve using tape or a glue gun. Remember your mask is only as good as the seal you make so be sure there are no leaks around the valve. The valve will also be reusable as long as it is properly cleaned.



FPR filters (Home Depot)

An exhaustive search of the internet could not turn up any quantified data regarding the FPR rated filters from Home Depot. The information suggested the FPR 10 rated filter (shown below) is equivalent to an MPR 1500 to 1900 rated filter. This unfortunately gives a very broad range and makes even rough estimations difficult.

I was also able to find an FPR 12 filter at a separate Home Depot but, again, could find no quantifying information online. I would assume this filter is getting closer to an MPR of 2200 to 2500 but cannot be sure. If these are the only materials available they will be better than nothing.

Be careful when reading packaging. The image below shows an MPR 2200/2250 filter with a comment at the bottom right that reads: “Traps 95% of airborne particles from 0.3 to 10.0 microns.” The issue here is it may trap 99.9% or particles from 1 to 10 microns but only 70% of particles from .3 to 1 micron. The broad range and lack of specific test condition criteria make comparisons very difficult. As an MPR 2200 I would expect it to fall half way between the MPR 2500 and MPR 1900 or about 69% for E1 particles (0.3 to 1.0 micron in size).





Filter Bypass

Bypass refers to the air passing through openings around the mouth and nose that is therefore not filtered. The formable wire will allow the wearer to mold the mask to their face shape to minimize bypass. If the form is not sufficiently holding a thicker formable wire is required.

Thank you reading. I hope this was helpful to you. In our current uncertain times this will hopefully allow preparation without undo financial burden. If you need these type of masks for work this will provide an alternative that will keep costs down as supplies run low or are completely unavailable.

If you felt this guide was helpful please donate at paypal.me/diyn95

PLEASE: Again please immediately share this information with your email contacts and anyone you feel may be helped by it. I don’t have the resources to push this website to the top of google and I am sure you will agree I am not the greatest website designer.