Why is the filter so large?

The filter is actually as small as it can be while still being able to perform effectively. The larger filter area makes it easier and safer to breathe than a mask with a small filter can. We are using high-performance filtration media and the surface area of the OSR-M1 Mask is already right at the limit of efficiency and breathability that we deem acceptable considering the current global situation. Any mask with a smaller filter cannot be providing adequate protection for the following reasons:

A larger filter area reduces the velocity of air passing through the filter media. Slower air increases the efficiency and reduces the breathing resistance of non-woven filter materials. The filter media works by both blocking larger particles, and using an electric charge to pull and latch tiny particles onto the filter fibers. Particles with lower kinetic energy cannot penetrate as far, meaning slower moving particles can be blocked more effectively. Similarly, slower air can pass through the filters with less resistance, making it easier to breathe. This is why our filter is as large as it is: to make it easier and safer to breathe.

Masks with smaller filter area force air to move faster through the filter; fast moving air reduces efficacy of masks. This is because for every breath you take, the same amount of air must pass through a smaller opening -- like putting your finger over the end of a water hose. Restricting flow causes fluid or air to move faster so that the same volume/mass of fluid can pass through in the same amount of time. This is the law of conservation of mass. In the case of small filters with fast moving air, particles carry more kinetic energy allowing them to penetrate deeper or past the filter before being pulled by the electric charge into the fibers.Masks with smaller filter area force air to move faster through the filter, reducing efficacy of a mask.

Something to be careful about is that many mask manufacturers have likely not done their homework and their masks are not working as effectively as they are stating. Often they will state a high efficiency filtration capability, but they are quoting from the filter manufacturer datasheet, rather than tested data from their mask. Filter manufacturer datasheets are usually showing data at 5.3-9.6 cm/s over a 150-200 cm2 filter area. To compare, our mask has an expected air velocity of 20-25cm/s due to the size of the filter. If that other mask you are looking at has a smaller area than the M1, then they definitely have a faster air velocity, and with that they definitely have lower efficiency performance and greater breathing difficulty.


How many filters do I need?

The lifetime of your filter depends on how long and how frequently you wear the mask and what you are exposed to in your environment.

If you are a front-facing worker who wears the mask for multi-hour shifts you may expect to replace the filters more regularly. You may replace the filter daily, or to conserve Filter Media, use the Wait & Reuse practice (see User Manual).

If you are not a front-facing worker and are instead an occasional wearer only using the mask to go to the store or on a flight, then leaving the mask hanging to dry until your next use is likely adequate. In such cases, we recommend a fresh filter at least once a month.

Is condensation inside the mask normal?
This is completely normal, and actually means your mask is fitting and sealing well to your face. All of your inhaled and exhaled air is passing through the filter, and nowhere else, meaning there are no leaks. Are you in a cold environment? Colder external temperatures cause more condensation inside the mask.

You can wipe out the condensation with a clean cloth, or disinfectant wipe. Be sure to clean your hands prior to wiping out your mask.
Does the filter work with condensation?

With regards to filtration efficiency and condensation: your filter will remain very effective. We are looking to collect our own data on this, but until then, we can look to published literature. Published data specifies the relative humidity at the filter after wearing a similar style of mask for 60 minutes stabilizes at lower than 88% [1]. The electret charge of the filter media, that provides the high filtration efficiency has also been shown to remain stable within 92.5% of it's rated value, even after holding at a constant 94% relative humidity for 18 days [2]. Those authors extrapolate that the filter electret charge should remain stable even up to 1 year for filters with similar fiber geometry to ours in those conditions. The fiber geometry of our filter is shown in the scanning electron microscope image below. The nominal 10-20µm diameter fiber width matches with the P1 fiber width described in [2,3].

The standard we have tested our filtration efficiency to requires conditioning the filters at 85% relative humidity and 38C (100F) for 24 hours before the test [4]. This means the testing criteria we are using for the OSR-M1 replicates conditions inside the mask during long-term wear both in terms of temperature and humidity. Our filter performance is tested at the operating conditions that exist inside the mask even when it is very wet and humid inside due to multiple hours of use of the mask.

Scanning electron microscope image of filter media.

[1] Cherrie, John W., Shuohui Wang, William Mueller, Charlotte Wendelboe-Nelson, and Miranda Loh. “In-Mask Temperature and Humidity Can Validate Respirator Wear-Time and Indicate Lung Health Status.” Journal of Exposure Science and Environmental Epidemiology 29, no. 4 (2019): 578–83. https://doi.org/10.1038/s41370-018-0089-y.
[2] Motyl, Edmund, and Bozena Łowkis. “Effect of Air Humidity on Charge Decay and Lifetime of PP Electret Nonwovens.” Fibres and Textiles in Eastern Europe 14, no. 5 (2006): 39–42.
[3] Blackburn, Camron. “Filter Media Database.” MIT Center for Bits and Atoms, 2020. https://camblackburn.pages.cba.mit.edu/filter_media/.
[4] NIOSH. “Procedure No. TEB-APR-STP-0059, Revision 2.0. Determination of Particulate Filter Efficiency Level for N95 Series Filters against Solid Particulates for Non-Powered, Air Purifying Respirators Standard Testing Procedure (STP),” 2019, 1–9. https://www.cdc.gov/niosh/npptl/stps/apresp.html.

What if I put a second mask under my mask to soak up condensation?
We do not recommend wearing a second mask inside the Facepiece for two reasons:
  1. This second mask may affect the quality of seal around your face, accidentally allowing through unfiltered particulates.
  2. A second mask will increase breathing resistance, leading to discomfort.
  3. Increased breathing resistance can also increase rebreathing residual CO2 that can lead to: discomfort, fatigue, dizziness, headache, shortness of breath, muscular weakness and drowsiness [1].

[1] Smith, Carmen L., Jane L. Whitelaw, and Brian Davies. “Carbon Dioxide Rebreathing in Respiratory Protective Devices: Influence of Speech and Work Rate in Full-Face Masks.” Ergonomics 56, no. 5 (2013): 781–90. https://doi.org/10.1080/00140139.2013.777128.

What if the filter is installed backwards?

The “unloaded” (e.g., used under non-industrial air conditions) performance of the filters is effectively identical in either direction, at ≥98.5% efficiency (we designed the mask to equally filter inhaled and exhaled air). It is only when the filters approach “loading” conditions, such as throughout an 8-hour shift of dusty work (e.g., demolition, or metal grinding), that there is a drop in filtration efficiency. In these maximum loading cases, the worst data shows a maximum 3.97% penetration, or 96% filtration efficiency—still pretty solid performance. For indoor use in non-industrial environments, this loading level is unlikely ever to be achieved.

There are four layers to our filters: spunbond, meltblown, technical, spunbond. The spunbond layer is mostly structural to hold everything together. The meltblown blocks larger particles to keep the technical layer operating in its most efficient range. The meltblown layer forces the small particles to bounce around, reducing their kinetic energy, and slowing them down. Slower particles get caught in the electric charge more easily. This is also the same reason why we have such a large filter area, so that for a given breath the air moves slower, making it easier for the electric charge of the filter to grab particles out of the air.

The technical layer is called an electret non-woven polymer because its fibers hold electric charge. The static-electric charge on the thin fibers that make up this layer pull the smallest of particles out of the air. It is like why dust sticks to a statically charged balloon, or you can think of it as a tractor beam from Star Wars, operating at a microscopic level. By using static electricity to pull particles from the air, larger gaps can be left in the filter, making it easier to breathe through while maintaining high filtration efficiency.

The filter performs differently one way than the other because it has a special layer included on the outer side of the filter to reduce the kinetic energy of particles and to prevent clogging up of the specialty electret technical layer of the filter.

Sample layup of the OSR-M1 filter media.

What happens if the filter is installed backwards is the dense sheet that blocks large particles and reduces the kinetic energy of small particles is not able to protect the technical layer. This means the technical layer gets loaded up and is not as effective at pulling the small particles from the air. The following plots are from NaCl load tests on our filters. These tests are run following the TEB-APR-STP-0059 protocol outlined in the Testing and Specs page. A 200mg challenge load of NaCl particles with a count mean diameter of 0.075 ± 0.02 µm is forced through the filter body at a flow rate of 85L/min.

Filter NaCl challenge test, oriented correctly.

This first picture shows data collected during a loading test of our filters when oriented correctly. As the meltblown material loads up the breathing resistance increases, while the particle penetration remains relatively unchanged. After about 18 minutes the full load of particles has been used up, and the test is over. Unfortunately, it is difficult to map this test directly to allowable usable time of the filter, but in general it is used to specify a full work shift.

Filter NaCl challenge test, filter oriented backwards.

This second plot shows what happens when the filter is installed backwards, and the meltblown material is sitting behind the technical layer. Here the particle penetration increases rapidly while the resistance slowly climbs. The reason the filter efficiency is dropping is because the technical layer is loading up and the particles have not yet been slowed down by the meltblown layer. Even in this backwards configuration the penetration remains under 4%, meaning the filter is still blocking 96% of even the smallest particles.

Why do I need to assemble my mask when it arrives?
We chose to ship unassembled masks for two reason:
  1. to reduce your cost,
  2. to acquaint you with a procedure you’ll need to do regularly to keep your mask clean and disinfected.
We figured before you throw-out the instructions, and while we have your attention, it would be a good teaching moment to introduce each of the components. This way you can build some confidence in how the pieces work, how to clean them, and how to inspect and repair the mask if ever there were a problem. We do realize this causes some inconvenience, but we hope the assembly videos here make it a bit easier.
Does the mask fit correctly if my chin is all the way inside?

Likely it does fit, but please check that you have a good seal as described in the User Manual.
Your chin and lips resting on the inner Facepiece is actually correct. In order to reduce re-breathing residual CO2 from your previous exhale, we try to reduce the space between your mouth and the mask. Re-breathing CO2 though not a mandatory specification, does affect your comfort and health[1]. If you notice the Lock Ring spokes are dished inward to give lips a little more room.

[1] Smith, Carmen L., Jane L. Whitelaw, and Brian Davies. “Carbon Dioxide Rebreathing in Respiratory Protective Devices: Influence of Speech and Work Rate in Full-Face Masks.” Ergonomics 56, no. 5 (2013): 781–90. https://doi.org/10.1080/00140139.2013.777128.

What diameter is the filter?

The filter is 105mm in diameter, and the mask can accommodate a compressed filter height of about 3mm.

Are you looking into adding additional filtration media, or advanced functionality? The filters we provide are already performing at about 99% filtration efficiency of particles ≥0.075µm with breathability specs well within allowable ranges. It's hard to do much better than that. If you were to add additional filters it may affect overall breathing resistance, which could make breathing more difficult, and affect residual CO2 inside the mask. That said, we've also been looking into additional advanced functionality and will likely release some upgrade filters in the future. However, for the time being we are laser focused on achieving certification of the mask for standard particulate requirements so that we can expand the user base and confidence in the mask.

What is the origin story of Open Standard Industries?
We started this project on Helpfulengineering.org, a global hackathon that spontaneously formed at the beginning of the pandemic. What was initially a team of 50+ people was corralled into a small team of consistent and effective contributors -- nearly all of whom remain involved to this day. That team made a massive push and developed the OSR Model 1a between March 21, 2020 and May 13, 2020. The team then formed into the non-profit Open Standard Respirator in order to find partners to scale mask production. Over the summer we identified a candidate filter layup that demonstrated passing performance. However, it turned out over the summer of 2020, a lot of funding enthusiasm to make masks had dwindled. Based on the news we were seeing, we felt it important to keep pushing. It looked like we would not yet be done with needing masks, and, winter in particular, would require high-performance masks. In order to make masks at scale and have a chance of achieving certification we found it necessary to build a corporation, Open Standard Industries, Inc. One of our co-founders and now CEO Dr. Matt Carney, was a recent phd graduate and postdoctoral associate at the MIT Media Lab Biomechatronics Group. He built a couple websites to publicly track progress of our efforts. For historical purposes those previous tracking sites are listed here: