In Germany, the wearing of medical masks, i.e. FFP2 or surgical masks, became mandatory yesterday. Since I don’t think anyone will check certifications in public, this means that everything except cloth masks is allowed. I’d like to explain how masks work, how filter and fit determine their efficiency, and why a cloth mask ban doesn’t really make much sense to me. Furthermore, I’d like to point out solutions for a more responsible, safe and sustainable use of medical masks. One of these solutions could be wearing a cloth cover over medical masks, or double masking.
Table of Contents
(1) Mask Science: How do Masks work, What are special properties of Medical Masks and Cloth Masks or Covers?
(2) Problem and Solutions: Home Tests for Masks, Reuse of Disposable Masks and Improving the Fit of Masks
(3) Double Masking: Hybrid Cloth Masks on top of FFP2 / KN95 Masks and Surgical Masks, plus Practical Tipps
Let’s start at the Beginning…
I’ve studied clothing design with a focus on patterns, but worked mainly as an illustrator since. Last spring, I intended to sew a couple of masks for friends and family, so I tested all the patterns I could find. None of them fitted properly, so I used what I learnt to invent my own. Surprisingly, the first attempt was a perfect fit – gapless / fog-free, with space to breathe / speak and even reliably staying in place! To help others, I published the pattern, and ever since, the “Luckhaus Hybrid Mask” is enthusiastically sewn by volunteers and partners from all over the world. Meanwhile, I’ve helped countless makers, created a pictorial, customizations, instant masks and an infographic for mask tying.
My expertise is pattern making, not material science, but after spending a lot of time reading and discussing studies and articles, I’ve learned a bit about how masks work. On this basis, I am writing here, to the best of my knowledge.
The recent representation of cloth masks in German media vexes me. It is claimed that cloth masks “do not filter” or that “all air escapes to their sides”, whereas medical masks are presented as perfect protection, under all conditions. From what I know, that’s simply wrong – and making medical masks mandatory just doesn’t make sense to me.
I don’t write this post in order to sell masks or anything like that. If you like my pattern, you are very welcome to sew / staple it for yourself, family and friends without me earning anything! I’d simply like to clarify misunderstandings, spread the education that I miss elsewhere, and basically encourage a more responsible use of all types of masks.
How do Masks actually work against Viruses?
Masks filter the air we breathe and thus protect the wearer from inhaling and/or exhaling dangerous particles. Even very simple masks can catch bigger droplets, while filtering finest particles such as aerosols is more complex.
The filter efficiency of masks is not only determined by (a) their material, which should let through as few particles as possible but as much clean air as possible, but also by (b) the gaplessness of their fit. If there are gaps around the nose, sides and chin, the air you breathe – and the particles it contains – can flow in and out unhindered. This air flow can be seen very nicely, for example, with fogged glasses! Foggy glasses clearly indicate a leaking mask.
Viruses are very small. The coronavirus measures about 0.1 micron (μm), and 1 μm is 1/1000 mm, so the coronavirus measures 1/10.000 mm. Viruses are typically emitted as part of a droplet, and in the air, they are clumped with salt and protein. There is a lively discussion in the scientific community about what size of particles contributes most to Covid transmission. It’s unlikely that particles below 0.3 μm matter, since with such a small volume, they can’t hold enough virus. The American N95 mask standard tests for 0.3 μm particles, while the European standard for medical masks tests for 3 μm particles. While this is important, test results don’t matter much if the air goes around the mask rather than through it! Gaps that allow the air to escape can hugely undermine the tested (!) effectiveness of a mask.
If you hold fabric to the light, you’ll see the tiny holes that are created by binding threads. These holes are quite large and elastic in knitted fabrics such as jersey, but smaller and more stable in woven fabrics such as poplin. Medical masks are not made from threads, but from spunbond (S) or even meltblown (M) polypropylene fibers, so even under a microscope, holes can be hard to detect. For medical masks, 3-5 layers of non-woven polypropylene are placed on top of each other (e.g. S-M-S) and often provided with electrostatic charge. Filter effect and breathability are stunning.
Unfortunately, it is not possible to achieve such a filter efficiency with commercially available fabrics and fleeces. However, we can at least use the underlying principles to optimize the filter effect of fabric masks – for example, by using fabrics that are as tightly woven as possible (600 TPI +) and the “Swiss Cheese Principle” or “Tortuous Path”, according to which the superimposition of several leaky layers leads to a relatively impermeable result.
Figure: Table 1 from “Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks“ by Konda et al. Due to air flow issues, results for specific materials may not be correct, but the comparison of “no gap” and “with gap” shows clearly. Other studies can be found on Smart Air Filters or Mask FAQ. FMVIZ even offers a calculator!
What are the special Properties of Medical Masks?
N95 / KN95 masks are particle filtering half masks for medical professionals. FFP and CE marks indicate masks that filter at least 95% (N95, FFP2, KN95, KF94) or 99% (N99, FFP3) of test aerosols in the EU test. In hospitals, employees train how to use N95 masks, and they’re specifically adapted to the wearer in model and size. The correct, gapless fit is checked in annual Respirator Fit Tests. Given these conditions, filtering face pieces offer excellent protection.
Without training, special adjustment and proper testing, it is – to say the least – difficult to achieve full filter efficiency. N95 / KN95 masks are made of particularly dense material and if they are not gapless, air will flow in and out through the gaps, unfiltered. As a result, masks may lose up to 80% of filter performance (see table above; even a gap as small as 1% of surface area of a N95 rated mask reduces filtration down to below 15% of smaller airborne particles!).
Just like N95s / KN95s, surgical masks are made from multilayer synthetics, which aim to be non-permeable for particles, yet keep breathing resistance as low as possible. These materials are often electrostatically charged, to attract particles. Since this electrostatic charge is highly sensitive to moisture, medical masks can’t be washed.
Surgical masks are made to protect the wearer and others from exhaled droplets, and to prevent infection from contaminated hands. The CE mark indicates masks made from a material with filter efficiency proven in an EU test. Due to their loose fit, a large part of air inevitably flows in and out of the edges. The protection is therefore limited.
Commercially available N95 / KN95 masks are usually one size only, and therefore don’t fit well on everyone.
When buying medical masks in the EU, look for the CE mark and the following four-digit ID number of the certification body. The certificate is issued in accordance with specifications of the European norm EN 149: 2001 + A1: 2009 or EN 149: 2009-08 for filter performance and fit, and issued in accordance with EU regulation (EU) 2016/425.
Unfortunately, I haven’t found any filter efficiency tests for non-certified, paper, one-layer or even counterfeit medical masks. Counterfeit likely circulates in high numbers, and for the general public, they’re extremely hard to detect.
For this reason, the CDC published a long list of NIOSH-approved N95 Particulate Filtering Facepiece Respirators. If you’d like to know more about NIOSH, FDA and ASTM standards and testing, you’ll find a roundup on the Filti page. Devon Ostrom compiled a list with some more useful Tips for Purchasing FFP2, KN95 and N95 Type Masks.
What are the special Properties of Cloth Masks or Face Covers?
Cloth masks are a broad field that can hardly be defined uniformly – except perhaps, that cloth masks are easy to use. Thanks to their washability, they enable those who cannot afford to constantly buy new medical masks, as well as those who want to avoid plastic waste, to protect themselves and others affordably, sustainably and hygienically.
The term Cloth Mask doesn’t only apply to loose fitting models with low filter efficiency, such as single-layer jersey masks, or models with medium filter efficiency, such as the classic two-layer cotton poplin mask, but also to snug, gapless fitting models with three or four layers that might even have a surprisingly high filter efficiency.
In March, when masks were scarce everywhere, lots of Germans sewed their cloth masks at home too, but when masks became commercially available around May, that stopped. In other countries, people continued to sew, e.g. for donations or for sale. Therefor, materials, patterns and details were further researched, and evolved.
The WHO still recommends cloth masks for healthy people under 60 (it’s up to countries if they follow), and regularly publishes their recommendations. Currently, three tightly woven layer masks – with (a) an outer layer made of water-repellent material such as polyester, (b) a middle layer made of a filtering material such as non-woven polypropylene (NWPP) and a moisture-absorbing inner layer such as cotton – are recommended for effective protection.
In cloth masks, gaps are to be avoided too, yet they don’t reduce the filter efficacy as drastically as in medical masks. The material of cloth masks is usually more permeable, so even with gaps, a higher proportion of air is filtered.
Cloth masks come in very different shapes and a number of sizes, so anyone can find a mask that truly fits their face.
So far, there is no standard for homemade cloth masks, yet large manufacturers might apply for ASTM F3502.
The WHO recommendations are beautifully explained on MakerMask.org. And on FMVIZ, you can find a handy tool that calculates the filter properties of your favorite material combinations (3 layers, but without fit) online! Open Source Medical Supplies doesn’t only list a lot of different project instructions, but also offers some mask education.
What’s the Problem?
Medical masks are made from materials with high filter efficiency. The density of these materials means that air can flow in and out unfiltered through gaps around the edge of the mask. Cloth masks are often made from less filter-efficient material, but this means that even if there are gaps, the air is at least partially filtered. Cloth masks come in a huge variety of shapes, so there’s the option to avoid gaps by choosing patterns that perfectly fit your face anatomy.
Cloth masks are washable, making them easier to care for, more sustainable and cheaper, while medical masks are often incorrectly cared for. This not only adversely affects the filter effect, but dangerous germs can accumulate.
Some people really depend on N95 / KN95 masks, for professional and / or medical reasons, and for them, they should always be available. Commercially available N95 / KN95 masks often come in one shape and size only, which out of the box fits only on few people. It is difficult for the general public to detect whether medical masks are counterfeit.
Medical masks are undoubtedly the gold standard for healthcare professionals who have been specifically trained and tested. For the general public, improper use and fit object the obligation to wear them. Very most people will likely assume that by wearing a N95 / KN95 mask, they are fully protected – and adapt their behavior accordingly.
Personally, I miss a scientific explanation for the (German) obligation. As far as I know, there are no studies that show cloth masks being less effective than paper masks for the general public. The only thing I could find was a quote from Bavarian Minister-President Markus Söder: “If the virus becomes more dangerous, the mask has to get better”. I think that’s perfectly right in terms of content, but the consequence to make FFP2s mandatory in Bavaria is not.
All over the world, there were information campaigns about how to make cloth masks as effective as possible, and what to look for when buying. I still miss something like that in Germany! This would have been a reasonable point to start with, and a ban for inefficient models like one-layer jersey masks would also have made total sense to me.
|Kind||FFP2-/KN95 Mask||Surgical Mask||Paper Mask||Cloth Mask|
|Filter Material||Excellent||Very high||Questionable||Low to high|
|Certificate||Yes (CE)||Yes (CE)||None||ASTM (for Industry)|
|Fit||Necessary (Fit Test)||Gaps||Gaps||Broad Range|
||Mostly one size only||Mostly one size only||Mostly one size only||Broad Range|
|Price||Most expensive||Less expensive||Usually cheap||Varies|
How can I possibly solve this problem for myself?
For me and many others, the medical mask mandate means that from now on, in risky situations, we will only be allowed to wear masks that have very good filter properties, but due to their fit can ultimately be more risky than well-filtering and gaplessly fitting cloth masks. In order to protect myself and others effectively, I’m trying to find solutions how this obligation can be reconciled with a most responsible, safe and sustainable use of these masks.
Can I test at Home how efficient my Masks are?
There are some very simple tests you may use to test the filtering and fit of your masks at home! These tests are very useful if you sew masks yourself, but also if you want to check, compare and possibly optimize purchased masks:
Before you go out into public with a new type of mask, you should test whether – and under what conditions – you can breathe easily with it, e.g. when climbing stairs or walking around. If you are unsure, please ask your doctor!
This is how you can test whether – and where exactly – your mask has gaps:
★ Glasses Test: If your glasses fog up with a mask, it tells you that the top of the mask is not completely gapless.
★ Mint Test: If you eat a peppermint (e.g. Tictac) and it stings your eyes, the top of the mask does not fit snug.
★ Puff Test: When you breathe hard, the mask should bulge. All draft or movement along the edges indicate gaps!
★ Hand Test: To feel a draft or movement, place your hands around the edge of the mask while exhaling vigorously.
★ Gill Test: Have someone look at the sides of the mask from behind while you exhale vigorously. Gills show gaps.
★ Smoke Test: If you inhale smoke and exhale it inside the mask, you can clearly see the path of the air flow.
In order to find out whether your mask reliably stays in place, it’s better to not only put it on briefly in advance, but rather try to speak, laugh and yawn in it – and after that, you can run the tests mentioned above once more.
Here’s how you can test and compare how effectively your material is filtering:
★ Light Test: If you hold your fabrics or your masks up to the light, you can see how densely woven the fabric is.
★ Spray Test: If you spray water through a mask – or layers of fabric – to a mirror, you can well see the permeability.
★ We don’t recommend the popular Candle Test, as this only tests breathability of a mask, not the filter efficiency.
MakerMask.org presents the procedure for three more detailed, science-based DIY tests for material efficiency.
Fit Tests in hospitals determine whether the masked test person can smell intense odours of a certain particle size (e.g. saccharin). According to Act Laboratory, a similar test can be carrried out at home with Nag Champa Incense.
Can I possibly reuse disposable Masks?
Under certain conditions, yes, but please be extra careful about it! I’d strongly advise against wearing masks several times in a row. As a precaution, worn masks of all kinds should always be treated as if they were contaminated, and therefore only touched by the ties and never in the middle or – as is common practice – worn around the neck.
Possible contaminations by viruses and bacteria can be deactivated by drying medical masks for 7 days or by heating them 60 min. at exactly 80° C. If medical masks get damp or dirty, they lose filter properties and should be disposed.
The FH Münster offers a detailed, illustrated PDF on “Möglichkeiten und Grenzen der eigenverantwortlichen Wiederverwendung von FFP2-Masken für den Privatgebrauch (Possibilities and limits of the independent reuse of FFP2 masks for private use)”, which I’d like to recommend. There’s no English version, but you can use Translate.
What can I do to improve the Fit of my Masks?
Basically, every face mask should be as close to the face as possible, without constricting. With certain face shapes, mask models and tying variants, masks might fit like this right away, but for most, a proper fit needs readjusting.
As a first step, you should tighten the ties, so that they fit snug yet comfortable. On medical masks, the earloops can be shortened with slip knots (see below), attached at the back of the head with one or more (paper-)clips or even wrapped around ponytail or bun from both sides (see below). With surgical masks, you can knot the ties, as close as possible to the point where they are attached to the mask, and tuck in the excess material (“Knot & Tuck”, CDC video). If ties are long enough, they can be cut open and re-tied behind the head. I listed a wide range of Mask Tying Techniques in a separate post! There, you will also find special solutions for sensitive ears, glasses or hearing aids.
Figure: How to tie an adjustable sliding knot in four steps
Next, the nose wire should be pressed so that it forms gaplessly around nose and cheeks. With KN95 masks, it helps to smooth out the folding peak in the middle, and to shape the wire around a finger. If that is not enough, the nose area can be sealed a little better with double-sided adhesive tape or silicone strips (“bra tape”). For surgical masks that fit poorly around the nose, the top edge can be folded inwards, to form a reverse pleat that covers the nose.
A recent study by Clapp et al found that a surgical mask worn (a) normally – with gaps – filtered at 38.5%. They tested different methods for sealing the gaps, f.e. (b) tying the ear loops and tucking the side pleats filtered at 60.3%, (c) fastening ear loops all the way behind the head filtered at 64.8%, (d) placing a ring of 3 ganged rubber bands over the mask and around the ears (see picture above) filtered at 78.2% and (e) sliding a 10-inch segment of nylon hosiery over the mask filtered at 80.2%. This means that with carefully sealing the gaps, you can more than double the filter efficiency of a certified surgical mask! The CDC’s new recommendation for double masking is based on this study.
Besides knotted rubber bands or nylon hosiery, there are some other constructions that can seal a surgical mask, e.g. mask braces or fitters. We solve the problem similarly, with gapless cloth masks on top of KN95 or surgical masks.
Double Masks can combine efficient Filtering and gapless Fit
When in spring 2020, N95 and FFP2 / KN95 masks were in short supply even for medical professionals, so that they often had to make them last for weeks, I helped lots of doctors and nurses to sew masks based on my Hybrid Pattern as covers for their precious medical masks, and I was surprised how perfectly the Hybrid fitted on top of them!
With risk group in the family, we have to be particularly careful about protecting ourselves, and the usual FFP2 / KN95 masks unfortunately gape quite badly on all of us. Therefore, we’ve also started wearing Hybrid Masks as covers over our FFP2 / KN95 masks early on. Our top masks do not only reliably seal the FFP2 / KN95 masks gapless, which we consider most important, but also protect them well, so that the medical masks can be worn a little longer.
The Hybrid Mask is also suitable as a top mask for beard wearers, because when they’re tightly drawn, the side channels press protruding cheeks hairs much closer to the face, which drastically reduces the usual “beard gaps”.
In a separate post about double masking, I’m introducing our practice with the Hybrid Mask and FFP2 / KN95 or surgical masks in detail, with lots of practical tipps to make double masking most simple, safe and comfortable!
But is that allowed in Germany?
The German government decided to make medical masks mandatory, not visible medical masks – so, as far as I can tell, there is absolutely no reason to not wear a medical mask with a cloth mask cover for seal and protection!
If someone might complain (so far, this didn’t happen to any of us) that the top of our mask combos do not look like a medical mask, I’d refer to the visible double straps and have trained to lift one side of the top mask for a moment, with the medical mask staying in place. I also take the packagings of my medical masks with me, just in case.
Given time, I’m quite sure that double masks will soon be seen more often in Germany too, as they’re such a reasonable way to combine efficient filtering and a gapless fit – and thereby protect the wearer much better!
This post corresponds to my level of knowledge by August 8th, 2021 and as usual, if there is any new information, it will be corrected accordingly. And I am always very happy to receive comments, questions, tips and new studies :)
If you are curious now and would like to read more about Hybrid Cloth Mask Pattern, associated Pictorial Instructions, Instant Masks, Tying Techniques, etc., all links with pictures are available on my Mask Hub Page! ➔
Conditions of Use, Rights and Sharing
This post is more than welcome to be shared. Design, pattern and instructions of the hybrid mask are, however, protected by German copyright laws (© Iris Luckhaus | All rights reserved) and may only be used non-commercially. I’m always delighted to discover photos of hybrid masks with the tags @irisluckhaus and #luckhausmask! :)
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Great thanks to Matthias Klesse, Angelika und Reinhard Luckhaus, Sarah Rice, Matt Thomas, Devon Ostrom, Hope Rambo Metzler, Rebecca Ma Lau, Devon Rowland, Tim Pani, Andrea Haydon, Kiri Schultz, Ania Mitros and Horst as well as the countless volunteer seamstresses and seamsters (a.o. from various amazing Facebook groups) for instructive discussions, interesting studies, good questions, great enthusiasm and exciting tests, for reading and feeding this post and all the amazing encouragement! You guys make this dark time feel so much brighter to me.