Update on masks

22 September 2021 by Jennifer

Practical thoughts about masks, including specifics on the ones I’ve been using.

A lot’s happened since I last wrote here about masks:

  • It’s now generally accepted in science-world that the covid virus is airborne. (There was some outdated information going around for a while, including at the World Health Organisation.)
  • The Delta variant came along, and it’s much better at transmitting from person to person than the original covid virus was.
  • There are vaccines, which are doing a great job of saving lives and reducing illness. The vaccine reduces the chances of both illness and death – but not all the way down to “can’t possibly happen”. Even if you’ve been double-jabbed, you could still catch covid, pass it on to others, be a step in the evolution of the next variant, and potentially suffer some after-effects (“long covid”).
  • There’s been a lot more research about what kinds of masks actually work.
  • Originally, I was wearing a fabric mask I’d made myself. Since then, I’ve also experimented with bought ones.

So I thought it would be a good idea to do an update here, on where I’m at now and things I’ve found out.

Update on masks (background is a photo of a shaped, disposable mask)

Context & disclaimer

This is info for people who believe that covid is worth avoiding. I realise some people think it’s exaggerated or nonexistent, and that masks and/or the vaccine are harmful; I might write something that’s more for you another day.

Disclaimer: I’m just someone who reads a lot, understands maths & scientific method, and would strongly prefer not to catch covid myself – or at least to put that fate off as long as I possibly can. I will link to some useful sources as I go. And, of course, I’m bringing my practical experience of the last year-and-a-bit of making, fixing and wearing masks :-)

Some masks are better than others

To stop the floating particles which contain covid virus, we know now that you’d want a mask which fits properly onto your face. You want the air to be filtered through the mask, not going round the edges.

The common type of “medical mask” was originally invented to stop little spitty particles from coming out of your mouth to the front, and to protect your own mouth and nose from splashes of icky stuff. It doesn’t really try to filter the air you breathe. This is part of the explanation for why so many healthcare workers have died or got sick: often, their masks were this cheaper kind, letting in air and virus around the edges.

FRSM = Fluid Resistant Surgical Mask. Pic of a white rectangular mask, with folds along its middle and two ear loops.

It’s not that this kind doesn’t help at all. But there are better ones.

A recent study in a hospital

A very useful study took place around the beginning of 2021, looking at using different types of masks in a UK hospital. The paper itself is still at pre-print stage (i.e. not yet completed its “peer review”, which is when other scientists read it and comment), so it doesn’t count as established science. But here’s what it was indicating:

Study author, Chris Illingworth from the MRC Biostatistics Unit at the University of Cambridge, said, “Before the face masks were upgraded, the majority of infections among healthcare workers on the covid-19 wards were likely because of direct exposure to patients with covid-19. Once FFP3 respirators were introduced, the number of cases attributed to exposure on covid-19 wards dropped dramatically—in fact, our model suggests that FFP3 respirators may have cut ward based infection to zero.”

Covid-19: Upgrading to FFP3 respirators cuts infection risk, research finds, BMJ article, June 2021

That study compared the protection from a “fluid resistant surgical mask” (FRSM) with the protection from a “filtering face piece 3” (FFP3), also known as a “respirator”.

The healthcare workers on the covid wards had originally been using the cheaper, looser, “FRSM” medical masks when they went to look after the covid patients.FRSM = Fluid Resistant Surgical Mask. Pic of a white rectangular mask, with folds along its middle and two ear loops.At that point, the statistics showed that working on a covid ward made you more likely to catch covid, compared to the people who were only working on non-covid wards. Working on the covid wards was increasing people’s risk. Their protection wasn’t complete.

Then the workers on the covid wards were given FFP3s, the more protective type, which fits closely around the face:

FFP3 = Filtering Face Piece 3. A shaped white mask, seen from the front. Another similar one seen from the back, still in its plastic packet, showing two rubber bands which are designed to go behind the head.

Note: I’m not saying it was this exact same type of mask, because I don’t know which brand they used. But it would’ve been similar to this, with the same rating for how protective it is.

What happened next? The rate of infection went right down. Once they were wearing the better masks, their rate of infection was the same as the workers on the ordinary wards, where the patients didn’t have covid.

It still wasn’t “no infections” – but logically, from the numbers, it looked like “no infections caught on the ward“. The pattern suggested that any remaining covid infections which those workers did catch were picked up outside of work.

Here’s another article about the same research: Upgrading PPE for staff working on COVID-19 wards cut hospital-acquired infections dramatically.

I find this quite reassuring. If an FFP3 mask can protect people who are actually working day in day out with people who definitely have covid, then it has a pretty good chance of protecting me when I go into buildings as well.

Limitations of that study

It is worth noting though that the hospital research was done before the Delta variant became dominant in the UK in early 2021.

What difference might that have made?

There’s no suggestion that Delta is better than earlier variants at getting through masks, or around the edges; that would be the same either way. But it is likely that compared to earlier variants, you need fewer viral particles of Delta to get infected. So maybe a few particles did sneak around the FFP3s during the hospital research and didn’t infect anyone, whereas now that same small number would cause an infection. Because the study was before Delta, we can’t use its data to answer that question.

I would like to see a similar study comparing worker infections on covid and non-covid wards now, with everyone in FFP3s.

(I wouldn’t suggest repeating the study exactly the same, because that would involve making some people use the less protective masks. That would be unethical, now we know that healthcare workers ought all to have FFP3s.)

Mask factors

What’s important in a mask? Here’s a quote from Professor Jose-Luis Jimenez, one of the scientists I follow, who’s done a lot of research around aerosols, filtering etc.

Three things are important for masks:

  • Good quality filter, that removes aerosols when the air goes through
  • Low pressure drop, so that we can breathe easily through them
  • Fit well to the face, not leaving any gaps

Any mask will help, but variation is huge

Also: for mutual protection, you don’t want a valve in the mask which lets your out-breath out without filtering. That type of mask is meant for protecting the wearer from dust or other pollution, not for catching viruses. The difference is that dust only comes from around you, but viruses might also be coming from you. (With covid, you can be infectious and not know it, because the infectiousness comes before the symptoms.)

Masks outdoors?

Before the Delta variant became dominant in the UK, I had mostly stopped wearing a mask on the street. From the evidence which built up during 2020, it seemed as though outdoor transmission was such a vanishingly low risk, it wasn’t worth it.

But for Delta, there does seem to be some evidence that it can transmit outdoors. And it’s definite that Delta is more infectious in general – that’s exactly why it out-competed Alpha, the previous dominant strain in the UK.

I also like that by wearing a mask on the street sometimes, I’m showing solidarity with people who are more vulnerable, by implicitly affirming that it’s no big deal to be wearing a mask these days when out & about.

So I’ve started again – sometimes. I don’t if no-one else is around. And if I’m with friends whose judgement I trust about the risks they’ve taken recently, and there’s a breeze blowing, I might not then either.

On to masks I have tried!

Fabric mask for outdoors

For walking outdoors or cycling, I still sometimes use my original blue fabric face mask. It has the fixings that go behind my head, and I like how easy it is to flip down to my chin when I’ve got the street to myself, or back up when I want to.

Fabric mask, quite floppy. The main fabric part has a printed pattern of line-drawn white flowers on a mid-blue background. Its headband and neck band is made of a thin curled-up strip of lighter blue stretch fabric, with a knot on the neck-band side to set its tightness.

With experience, I’ve found that there’s a limitation of the fabric mask if I’m talking: as my chin goes up and down, the mask starts gradually wiggling down my face! And because its inside fabric is quite floppy, it’s more likely than the stiffer ones to flop annoyingly around my mouth. I think basically these are design flaws, and at some point I might experiment with different designs again. But neither of those limitations is a big deal if I’m not talking at the time.

The more important limitation is that I’m pretty sure the fabric mask won’t be filtering as much potential-virus as some of the other kinds now available. I’m a bit iffy about it now in a situation where the risk might be higher, e.g. indoors where other people’s breath might have built up.

For going inside buildings, I’ve experimented with three other kinds.


FFP2, Filtering Face Piece 2, I got from Boots: about £10 for a pack of 5, so £2 each.

FFP2 = Filtering Face Piece 2. Two white masks with ear loops, seen from the side. The one on the right is brand new and flat. The one on the left has been opened out. Its ear loops have knots in to make them a bit tighter. Its top edge has been trimmed to be about a centimetre lower.

If you compare my one on the left to the brand-new one on the right, you’ll see the one on the left has been slightly trimmed at the top. I found there was “too much of it” above the nose wire, so that when it felt correctly fitted on my nose, it came up too close to my eyes.

The bit I’ve cut away doesn’t affect the overall integrity of the thing. I just snipped it off carefully with scissors, making sure not to snip away the dotted “seam” which is part of holding the nose wire in place.

The photo shows that I’d also put knots into the ear elastics. This was because the mask felt a bit too loose on my face. The knots make it fit more tightly – which is less comfortable around the back of the ears, but reassuring in terms of covid risk :-)

A nice thing about these FFP2s is that they fit neatly into an A6 wallet for carrying around:

FFP2 fitting neatly in an A6 wallet. The mask is seen from the side, folded flat. It's in a transparent plastic wallet which has a popper to hold it closed.


Since I tried out the FFP2, I’ve also now acquired an FFP3: Filtering Face Piece 3. This is the same type as proved protective in that hospital ward study.

FFP3 mask, from the inside, showing the grey foam nose piece. Two red rubber bands go from one side to the other of it, held on by staples.

FFP3 is a better “standard” than FFP2. I found this page which summarises the differences, and has some useful info about particle sizes. (But note that some of the other info and guesswork on that page has been superseded by now – it dates from fairly early on in the pandemic.)

Here’s the ratings:

  • FFP2 must filter at least 94% of all particles 0.3 microns in diameter or larger.
  • FFP3 must filter at least 99% of those same particles.

Obviously how well either of them actually filters your air in reality does also depend on its fit to your face.

(Why rate them by how well they catch the 0.3 micron particles, and not by how well they catch a different size? Really nice explanation here of why 0.3 microns is the most difficult size to capture in a filter. If it’s managing to catch those, it’s probably doing a good job on the smaller and bigger sizes too.)

I find this FFP3 mask quite comfortable. It turned out to fit me well, and the better they fit in the first place, the less fiddling you have to do with them. The foam really makes a difference to the seal over your nose, and the shape of it means it doesn’t flop on your mouth when you’re talking.

Real or fake

A tricky thing about buying formally-rated masks is whether they’re fakes, made of lower-quality filter fabric which perhaps would let more particles through. I’d heard of that happening, and it was worrying me a bit, because how would I know? I wouldn’t have any way of testing. So my plan was to go to the actual 3M web site and click through to suppliers they listed.

None of the official suppliers was offering just one FFP3 at a time, or even just five, so getting these was expensive: about £115 for 20, so £5.75 each. On the other hand, a good thing about buying a boxful is being able to share them around to friends and family – which I have been doing :-)

Size adjustment

Although I was lucky with the fit, I’ve also done an adaptation to fit one of the FFP3s to someone else’s smaller face.

The mask was rather loose under the chin. I used my sewing machine to take a tiny “tuck” under the chin with a line of stitching, then snipped off the excess. I used close-together stitches to ensure that the join was tight, with no air gaps.

The initial snip left a slightly spiky edge of the material; a bit of very careful additional snipping took off that harder corner and left a softer edge.

Three photos in a sequence. First photo shows the chin of an FFP mask, with a line of stitching to take a tuck in the edge. Second photo shows how the mask is trimmed back next to the line of stitching. Third photo shows the seam from the inside, as you'd see if it you were about to put on the mask.

(Yes, there is some weird speckling on those pix, not sure why. Maybe my phone was too close to the magnet in the sewing machine motor.)

If I couldn’t sew, I’m not sure what the best way would be to take in the “tuck”. I’d be wary of using a stapler in case it didn’t sufficiently pinch the edges togther, or in case the staple-holes gaped slightly and let air through. On the other hand, a stapled line carefully supplemented with sticky tape would probably still be better than a too-big mask which was loose around the face.

Re-using “disposable” masks

Officially, both of those types of mask are disposable – but for each variety, I’m still on my first one. Because I mostly work from home, I don’t go to all that many places where I’d need one, so I never wear it for all that long at a time. And then I’ll air it by hanging it up, e.g. near a window in the sunshine. There’s no evidence the covid virus could survive a day like that.

Two disposable masks are hung from little silver-coloured hooks, in bright sunlight. One is an FFP2 type, the other is an FFP3 type.

For people who need to wear a mask more of the time, one thing I’ve seen suggested is to buy several and rotate them, so that each one has a few days to air before you wear it again.

(In fact, I aired the FFP3 quite a bit before I even wore it “for real” the first time, because the foam that goes over your nose smells rather plasticky. It’s worth taking out of the packet early when you first want to wear it.)

From looking at other people’s worn-out FFP3s, the likely failure points I’ve seen are

  • Nose wire gets metal fatigue and snaps in the middle. To put this off as long as possible, avoid folding and unfolding the mask when you’re not wearing it.
  • Rubber bands snap. (But see below for how to switch in replacement elastic.)
  • Nothing actually breaks, but the material gets gradually softer from use, and doesn’t hold its shape so well.

Eventually, they’d get grubby, too, if they hadn’t failed first. In my case, it probably helps that I don’t wear makeup, so there’s only normal skin-oils on my face to come off onto it.

As a way to slow down the metal fatigue from folding and unfolding, I sometimes pop mine in a little box when I need to take it somewhere. This means it can keep the shape of the wire while I’m not wearing it, rather than getting squashed in my bag.

An FFP3 respirator mask tucked into a small cardboard box. The mask is in an unflattened three-dimensional shape ready to be put on. It's white with a 3M logo in faint grey on the front, a CE mark "CE 2797" and a few other numbers..

Cambridge mask

More expensive initially, but of course cheaper in the long run, are commercial reusable masks.

I recently acquired one from the Cambridge Mask Co. This isn’t reusable for ever and ever: its filters are meant to last around six months, depending on how often you wear it, and how polluted the air is where you live.

Fabric mask. The edges and the ear loops are black. The main middle fabric bit has a pattern of multiple colours. Each side of the chin has a small elastic loop with a bobble thing for setting how much of the elastic is pulled into the loop.

Although this just looks like “any old fabric mask”, it actually has three layers of good-quality filtering. The makers sayOur masks meet N99 standards in the USA but FFP2 standards in the EU.

There are lots of different colours available, including tasteful dark ones; this design was just what they happened to have in stock when I wanted one.

Things I like about it, compared to the officially “disposable” ones:

  • Won’t wear out as quickly.
  • Seems more robust for being casually squished into a pocket and fished out again.
  • Washable, although the washing is said not to extend the life of the actual filter.
  • More options for how it looks.

Things which seemed less good:

  • I don’t like the ear-loop types, so for me this is less comfortable than the FFP3. It does come with an optional-extra separate back-of-the-head elastic to hook onto the ear-loops, but I haven’t found that to work as well as the types which have two back-of-the-head elastics as their “main” attachment.
  • More difficult to fit and seal. I had trouble at first getting it to seal below one eye. The nose wire is quite short, so its width doesn’t extend far outward past my nose. I did manage it eventually.
  • More expensive up front, obviously. But that pays off in the long run.

It cost £29.88 including shipping, and arrived pretty quickly. The mask itself was £24.95 of that. Anything over £30 is currently free delivery.

This company has been making masks since long before covid, originally to protect against air pollution – hence some of the older designs having valves where the out-breath isn’t filtered. For mutual protection from viruses, you don’t want a valve (as noted above).

Here’s an independent review of the Cambridge masks. That site has reviews of lots of other types too.

What if the mask was a risk itself

I’ve seen some concerns about masks themselves building up a lot of covid virus. Couldn’t that make them more risky?

I think probably not, not to speak of.

Firstly: if some virus did land on the outside of it, better there than in my lungs! In my lungs, it could get going. On the mask, the virus would just disintegrate after a while.

Secondly, even if I touched the outside of the mask while taking it off… that would only be a contact risk, not a breathing risk, and all the evidence I’ve seen suggests that for covid, breathing it in is the big risk.

Diagram showing aerosol particles coming from one person's mouth (the "Infected person") and spreading out into the air. The largest particles fall down, and the small and middle-sized ones float in the air, towards another person (the "Potential host"). The drawings of the people include a diagram of their lungs, and each of them has the particles dotted through their lungs, the first person more so. It shows that the second person has breathed in some of the air from the first person. A close-up of one of the first person's particles shows it has viruses in it.

(pic is from this paper)

I’ve got no reason to think that the virus could get into me through the skin of my hands. From there, it would only have even a theoretical chance if, before washing my hands, I poked my finger up my nose or into my eye or mouth, or handled food. The early-days “try not to touch your face” should’ve probably actually been “try not to put your finger up your nose or in your eye”.

And the fact is, I’ve not read about any examples of possible surface (“fomite”) transmission which weren’t later shown to equally or more likely have been airborne instead. The fact that the virus could be on a surface doesn’t mean it could infect anyone from there – and although that’s still theoretically possible, I’m yet to see proof it’s ever actually happened.

I still wash my hands anyway, but I’m not like “oh no, I might’ve touched something with covid on, that’s terrible”.

I could be wrong, but it seems to me that the “careful how you touch your mask” caution actually comes from experience with other diseases, or from handling poisons – and from a time when there was less knowledge about covid.

I do think it makes sense to wash your fabric mask every now and again, same as you’d wash any other piece of clothing, so it doesn’t get stinky, or, worse, mouldy. But I really don’t think it’s a covid risk to have a slightly grubby mask.

So yeah, I’m not bothering myself about any covid risk which comes from touching the mask. If there even is any risk from that, it’s minuscule compared to the benefit of having cleaner air to breathe.

(Likewise, all the cleaning doorhandles and suchlike is probably really good for reducing the number of other things people catch! But there’s no evidence it’s doing much about covid. People are carrying on doing it now because they’ve got used to doing it or seeing it – and, to be a bit cynical, because paying someone for extra cleaning is easier than improving the indoor air quality.)

Mask fit

How do you know if your mask is well fitted?

One of the clues I use is the feel of the mask on my face. If the fabric of the mask moves in and out just a little bit to match my breathing as I breathe in and out, or if I can feel the mask’s edges sucking just slightly more onto my face as I breathe in, those are good signs, because they show that the airflow is pulling through the mask fabric.

For people who wear glasses, another clue is whether your glasses steam up! That’s a bad sign: it happens when your breath is being channelled up past the top edge of the mask, meaning there’s a gap.

If you really want to be sure, the official professional method is to put on your mask or respirator, then release a strong smell of some kind into the space around you. If you can smell the pong, you know it isn’t fully sealed. But I confess I haven’t looked into this method in depth, and I’m not sure which specific substances are the right ones (because some types of pong are meant to go through the masks). Comments welcome from people who’ve actually tried it.

FFP3 ear-loop adaptation

Not everyone likes the elastics which go behind your head. Here’s one of the FFP3s adapted to use ear elastics instead:FFP3 adapted to use ear elastics. A shaped white mask seen from the angle where you'd be about to put it on, with a narrow grey foam strip across the nose area. It has black elastic ear loops.Ear loops typically don’t hold on to your face quite as well as the behind-your-head style. So this adaptation potentially makes the mask slightly less effective, because the seal might not be as tight. But as one of the experts said, “the best mask is one you’ll actually wear”.

The first step in adapting a mask this way is to remove the original staples. This is harder than it might first look, because they’re much tougher than typical stationery staples. I’ve used either a small screwdriver, or the type of staple remover which is like a blunt thin blade, and I found it takes a few careful minutes. The tip of a flat-head screwdriver pokes under the folded-down end of a staple, lifting it.

Then you can punch a couple of holes using a hole punch, to loop the elastic through. Obviously the holes have to be on the end part where the staples were, not on the main part which is actually filtering your air!

You could equally well use the new holes to add replacement behind-the-head elastics, if that’s what you prefer – for example, if you have one where the rubber band snapped while the mask itself was still OK.

At vaccination centres

The “basic” medical masks are still in use at UK vaccination centres, which in my opinion is a disgrace. If I were in charge, I’d seriously consider taking the opportunity to distribute FFP3s there, or at least FFP2s, even though it would be more expensive.

Then I would encourage people to take theirs home afterwards, and keep it. That would mean many more people having a decent quality filtering mask on hand for their riskiest situations, e.g. if someone in their house got sick.

And meanwhile, at the vaccination centre, it would help to ensure that no-one accidentally transmits or catches Delta while going for their jab, which I do consider is a risk at the moment.

At the moment, you might find that when you arrive at a vaccination centre, you’re given one of the “basic” ones and told to wear it, with the justification “everyone has to wear the same one”. (And in fact, the first time I went, they actually had people taking off masks indoors in order to switch from one type to another, which makes no sense. How many people had breathed unprotected into that corner of the room that day??!)

To be fair, I can see why volunteer stewards would be told not to get into discussion about individual masks. But to me it’s obviously silly to remove a better one just so as to match everyone else’s basic one. So what I did was put the “basic” one over my own. Not very comfortable physically, but it was only for a few minutes.

Elastomeric respirators

A type I haven’t tried yet, but would be interested in, is the “elastomeric” ones, with a reusable plastic section and a replaceable filter in the middle. “Elastomeric” means the kind of squidgy rubbery texture which springs back, a bit like the edge of modern swimming goggles. The squidgy edge is supposed to make it fit better to your face.

Prof Jimenez, whom I quoted above, currently recommends the Envo-mask. However, that brand is US-made and I’m not sure you can get them in the UK.Photo of an Envo respirator. It has a partly-transparent blue plastic frame, which would cover the lower part of a person's face, and the white filter can be seen through the front grid. It has straps to go round the back of a person's head. It's shown next to a black storage case just slightly bigger than the mask.

I’ve seen nominally similar things from other companies, but they don’t look as neat – more like old-fashioned gas-masks. Some are said to be very comfortable physically, though.

Masks for musicians

Before I leave this subject, here’s a bonus section for the musicians…

For string players, it’s mostly about which mask is comfortable and doesn’t get too much in the way – not really anything special to playing strings. It’s wind players who have a tricky challenge to keep their airborne germs to themself while playing!

At the mouth end, you really want a shape which will seal around the instrument mouthpiece, so that as you breathe in, you’re breathing in through the mask materialnot through the hole where the instrument comes through your mask.

There’s also the question of where the air comes out of the instrument. For things like horns or trumpets, the air comes out the other end, allowing for a simple cover over the bell. With woodwind, air can come out along the way as well, depending on which finger-holes are covered; some people have used a sort of bag-cover for the whole instrument.

Musicians Improvise Masks for Wind Instruments to Keep the Band Together.

I’m not convinced any of those wind-instrument masks is comparable to a properly sealed one, though, so it would be especially important to think too about distancing and ventilation – which is a good plan anyway.

Summing up

  • You could still catch covid even if you’re double-jabbed.
  • The virus can travel by floating around in the air, including across rooms, including staying in the air for a while after the people left.
  • The main risk factor is breathing in air which someone else breathed out.
  • Besides comfort, what makes a mask “good” is partly how well it fits to your face, and partly what it’s made of.

Wishing everyone luck with not catching anything :-)