Patient Knowhow

You may need a better mask for Covid-19 variants and Wildfires.

Here's how to upgrade to one that meets N95 standards or with high-fit/filtration (Hi-Fi).

Coronavirus and its variants such as delta travel in the air and collect indoors. These viruses are spread by aerosols (tiny particles) that are exhaled and inhaled also known as airborne transmission. The risk of infection can be greatly reduced by use of high-fit/filtration (hi-fi) masks that meet or exceed N95 standards. Patient Knowhow and our partners have discussed hi-fi masks in a number of recent news items in CBS News, Boston Globe, Marketplace Radio, CNN, Stat News, Harvard Business Review, and Washington Post. Among the safest and most effective hi-fi mask options available are N95 masks, elastomeric N95 (eN95) and others that offer these five key protective attributes: high filtration, superior fit, durability, breathability, and quality control. What’s most important is fit and filtration when exposred to toxic particles in the air. So the N95 mask that is fits your face best is probably a good choice. Without proper fit, unfiltered air will leak around the edges due to lack of tight contact with the face (in other words "no fit no filtration"). Many good options are available off-the-shelf -- when in doubt NIOSH approved masks are validated by the US government (see below). Below are a short list of off-the-shelf options you can purchase online as well as a number of new mask designs that push the envelope in these dimensions. Please also see notes on testing and valves below. If you know of any masks that should be included here please reach out to me at sri at patientknowhow dot com or @sri_srikrishna on Twitter. Here are our research publications and op-eds on controlling pandemics. For updates please join our email list.

N95 (CDC-NIOSH approved) Hi-Fi masks

Masks that are N95 (or better) approved from CDC NIOSH means the mask's fit, filtration, breathability, durability, and manufacturing consistency have all been rigorously verified by the US federal government. NIOSH maintains a list of approved masks and counterfeits. OSHA requires these same masks (N95 or eN95) for their inspectors.


Best thing about it: Silicone faceseal makes it easy to form a good fit when used with tightened head strap Approval: N95 (US, CDC-NIOSH)

Disposable N95 mask, NIOSH-approved, that builds on the traditional N95 design by using silicone to form a seal with the face.

Their video does a good job of explaining why in addition to the filter material a proper seal is important.


Best thing about it: Gel faceseal makes it easy to form a good fit when used with tightened head strap
Approval: N95 (US, CDC-NIOSH)

Reusable N95 mask, NIOSH-approved, that uses a silcone gel to form a seal around the face written up in Wall Street Journal and has test results.

Now ships with a plug for the exhalation valve (vent) and the plug is also available for purchase separately

The best thing about Envomask (1 minute video)

One nurse's experience after 7 months using Envomask

Unboxing and Assembly of Envomask

3M Elastomeric

Best thing about it: Shape of stretchy material forms a well-fitting faceseal with head strap, rugged design protects the filter and is long lasting
Approval: P95 or P100 available depending on the filter (US, CDC-NIOSH)

Reusable N95 mask (eN95), NIOSH-approved, with matching P95 filter sold separately.

Please also see notes on valves below. CDC reports that 3M now has a cover for the valve.

It was recently adopted by the Fire Department of New York using a higher filtration filter (P100) that is significantly harder to breathe through but offers even greater protection compared to the P95

The woman in the picture of this article appears to be wearing a 3M elastomeric mask but with a fuzzy cover over the filter to make it look a little less industrial and more stylish.

Fire Department of New York's video about the 3M elastomeric mask

Assembly and wearing a 3M 6000 series elastomeric mask

GVS Elastomeric

Best thing about it: Secure facial fit with elastic head straps, more condensed filters for better visibility, surprisingly breathable for a P100
Approval: P100 (US, CDC-NIOSH)

Reusable P100 mask (SPR451 Elipse P100), NIOSH-approved, that has a better fit due to the combination of its design elements, two adjustable straps. Note P100 has even better filtration than N95.

Please also see notes on valves below.


Best thing about it: Unique shape with nose pad creates a secure fit making it one of the best fitting disposable hi-fi masks
Approval: N99 which exceeds N95 (US, CDC-NIOSH)

Disposable N99 mask (Segre N31000), NIOSH-approved, that has a better fit (without use of gel-like materials) due to the combination of its design elements: vertical fold, two adjustable straps, and soft pad underneath the metal nose bridge. Note N99 has even better filtration than N95.

Their video does a good job of explaining why in addition to the filter material a proper seal is important and how it is measured with a Portacount device.

Available on Amazon and Acetool.


Approval: N95 or N100 depending on model (US, CDC-NIOSH)

Disposable N95 mask, NIOSH-approved, that builds on the traditional N95 design by using foam to create a seal with the face.

Comes in N95 and N100 varieties

Their video explains how to fit the respirator to the face.

N95 (disposable)

The N95 mask (NIOSH approved) is one of the best known high-filtration masks. Disposable N95 masks have been largely reserved for healthcare workers because they have been in short supply during the pandemic (although some manufacturers say that demand from the general public is beneficial to even out the ebbs and flows of demand from hospitals).

With some exceptions like the models above, most disposable N95 masks do not have special technology other than the filter material from which it is made to improve the fit to the face. Professionals use disposable N95 after training and a “fit-test” that assures proper fit to the wearer, something that would not be easy for most people. One study found certain N95 models passed fit testing more often than others. The current CDC director, Dr. Walensky commented in the Journal of the American Medical Association that, "N95 masks with suboptimal fit still had comparable filtration efficiency of more than 90%." One study of community participants found that with no fit training or testing, N95 masks were still much more effective at filtering PM2.5 (tiny particles) than surgical masks, and another study found a majority of untrained, inexperienced subjects were able to achieve a fit factor of 10 most of the time.

Some N95 models are also available from Amazon, Costco and Office Depot.

The FDA recently declared there is no longer a shortage of disposable N95 masks so their decontamination is no longer necessary. They prefer use of new N95 models instead of decontaminating older models that maybe hard to find. They also recommend use of reusable, elastomeric N95.

eN95 (reusable, elastomeric)

A reusable, NIOSH-approved N95 type of mask that is not in short supply is an elastomeric N95 (eN95) mask made by several manufacturers including 3M, Honeywell, MSA, etc.

According to the CDC, elastomeric models have sealing surfaces and adjustable straps that can accommodate a better fit, and the replaceable filters in some models could be used for one year as long as the filter cartridges remain in good condition.

We wrote about eN95 with our partners in August for the California State Firefighters Association, in October for Harvard Business Review, and in December for the International Assocation for Police Chiefs.

eN95 advantages of fit compared to disposable N95. In one study involving 60 participants by the Australian Society of Anesthesiologists, 98% of elastomerics passed fit testing versus 57% of disposables (Table 1). This suggests that (in general) it is easier for end-users to form a face seal with an elastomeric than a disposable. In one study published by the American Medical Association, the differences were less pronounced, 92.2% of particpants passed fit testing with elastomerics compared to 88.5% using disposable N95, and in another study participants performing CPR experienced leaks while using disposables but retained the fit while using elastomerics. A trauma center found that in 105 fit tests conducted, emergency physicians using elastomeric respirators passed fits tests every time. Whereas few disposable masks passed fit testing in a study of several models on one person.

MSA Safety has a video case study of the practical aspects of using elastomerics in a large hospital system (Allegheny Health Network) including cost compared to disposables, cleaning, and comfort for frontline workers. Includes interview with with end-users and surgeon, Dr. Chalikonda.

Please see notes on valves below. FDA and CDC have recently highlighted elastomeric (eN95) masks without valves.

Hi-Fi masks (either pending or not seeking N95 approval from NIOSH)

Also see the 10 winners of the Phase 1 of BARDA's Mask Innovation Challenge


Best thing about it: Better fit and greater breathability due to large surface area from novel origami design, made of high filtration materials

Uses a folding design based on origami principles to achieve a tighter fit with the face

Winner of a competition run by Johnson & Johnson and BARDA and recently written up in National Geographic.

Although not yet NIOSH approved they are working towards approval with test results.

Notably in their testing the filtration exceeded 99% (> 95% required), breathablity (pressure drop) is close to 4 mm of H20 (25mm maximum required, lower is better), and fit factor exceeds 200 (100 is required, higher is better).

Fix The Mask

Best thing about it: Turns any loose-fitting 3-ply surgical mask into a better mask that fits well, lower cost solution compared to disposable N95

A brace or harness to improve the fit of commonly used surgical masks.

Although not yet NIOSH N95 approved, when combined in a system with Armbrust surgical masks they have been listed on CDC's website as conforming to the Workplace Performance Plus standard with 97% filtration efficiency, 13 mm H2O pressure drop, and leakage ratio of 37.

Their video explains how to fix the face seal of loose-fitting surgical masks.

How to wear the brace (EMB) with a surgical mask.


Best thing about it: Solid fit, decent breathability, no valve, used by first responders across the state of Wisconsin and beyond

An elastomeric mask which is in use by first responders. Made by a Wisconsin auto-parts manufcturer. Uses a symmetric, flat-filter design (so no exhalation valve).

Although not yet NIOSH approved they are working towards approval.

Can be purchased on Amazon in small and medium sizes.

Open Standard Industries

Best thing about it: Solid fit with head straps, no valve

An elastomeric mask that uses a symmetric, flat-filter design (so no exhalation valve).

Although not yet NIOSH approved they are working towards approval with test results.


Best thing about it: Transparency to see smiles and facial expressions, solid fit with head straps, used in healthcare settings

Clear face mask with high-performance filter for better view of facial expressions

Has test results and updated test results . Although Canopy is not yet NIOSH approved they are working towards approval. Notably the inhalation resistance (10mm) appears to twice the exhalation resistance (5mm) which are both quite decent, and the 98% filtration efficiency exceeds the 95% in N95. The test graph shows the filtration efficiency increasing over time because the salt used in testing fills up the gaps. This is an NaCl loading test over 45 minutes with a very high load of salt to determine whether the efficiency degrades or increases, and by increasing it means the filtration remained intact for the duration of the test.

KF94 (disposable)

Best thing about it: Low cost, breathable, decent fit but fit could be improved further with fixthemask
Approval: KF94 (South Korea)

Another commonly used hi-fi alternative to disposable N95 is KF94 from South Korea. Aaron Collins has done some testing of various KF94 masks.

CDC (NIOSH) has actually evaluated one model of KF94 (Dr. Puri) with test results which show "initial filter resistance" of 8 to 9 mm of H20.

KN95 (disposable)

Many people use an alternative to disposable N95 called KN95 which is a Chinese standard for hi-fi masks. However there have been reports of inconsistent filtration performance so we are unable to make any conclusion about them at this time.


The CDC recently recommended use of two masks to improve fit (cloth mask) and filtration (surgical mask). This double-masking practice was reported by CDC to be an improvement over either type of mask alone. However a new paper on filtration efficiency of CDC’s double-masking found it was not even close to N95 with only a marginal benefit over single mask. So we are unable to make any conclusion about them at this time.

Additionally comfort, reusability, scalability, and style are desirable as we first identified with our partners in June (2020) in "We Need Better Masks". At Patient Knowhow we have been on the lookout for better masks with these properties. Which is best? We are not making any recommedations because it seems the right mask for each person is different based on their preferences, but at minimum they need to promise N95 level filtration and have features to form a seal (fit) with the face.

Valves: To protect others many N95 models with a valve require a workaround to cover their exhalation valve, although the CDC recently reported the maximum particle emissions through the valve are similar to or better than surgical masks or unregulated face coverings. Based on this CDC advises "In general, individuals wearing NIOSH-approved N95s with an exhalation valve should not be asked to use one without an exhalation valve or to cover it with a face covering or mask." Some manufacturers now address this by completely plugging the valve (e.g. Envomask and MSA). Additionally, valveless elastomerics and bidirectional high-fi masks designed for public use are also becoming available.

Testing: Places such as Nelson Labs do testing, and NIOSH has a certification process. Watch the video below by Minute Physics and read these recent papers (1, 2, 3) to learn why it matters.

Usage of Hi-Fi masks: Although 77% of people in the US reported using masks daily, only between 14% and 38% are using masks with these properties according to a national survey that Patient Knowhow conducted in December.

Disclaimer: These links to resources on masks, videos, or any information on this website (the “Content”) are for informational purposes only and should not be construed as professional advice. The Content is intended to complement, not substitute, the advice of your doctor. You should seek independent professional advice from a person who is licensed and/or qualified in the applicable area. No action should be taken based upon any information contained in this website. Use of the website is at your own risk. Patient Knowhow, Inc. takes no responsibility and assumes no liability for any Content made available over this website.

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