Mask Fit

Last updated 2021-04-02

Here are four questions to answer when assessing your mask. Fit and breathability can't be assessed until you have purchased the mask. We acknowledge the difficulty this causes, and that these are subjective and challenging to assess.

What makes a good mask?

How many layers does it have and what are the materials? A sandwich of two outer layers of cloth (cotton may be best) and a middle layer of ~70 gsm (2 - 2.25 oz/square meter) polypropylene, or two middle layers of lighter weight polypropylene. Manufacturers (in Canada) are not permitted to make filtration claims for masks but they are allowed and encouraged to specify what materials are used.

Is the material breathable?  Less breathable material will pull in when breathing in and puff out when breathing out. There may be a sensation that it is hard to breathe. The concern is that if the fabric is less breathable, air will take the path of least resistance around the edges of the mask. This completely unfiltered air is called edge leak. Some, but not all, high-threadcount fabrics, such as batik, have low breathability.

Is there a good subjective fit? Do you see gaps under the eyes or at the sides? Is there good contact with the face over the cheeks and along the jawline or under the chin? When you breathe in and out, is there obvious leak under the eyes, at the sides, or under the chin? A nose wire helps reduce leak under the eyes, but we recognize that completely eliminating leak in this area is challenging.
 

Are the head fastenings secure? This goes back to fit. Does the edge of the mask make good contact with the face and stay in position, or does it feel loose and move or fall down as you move or talk? Earloops are popular and convenient, but fixed-size earloops will only work well if they are the right size for your face. Adjustable earloops get around the issue of fit: however, there is some evidence that ties over the head may improve the overall filtration of a mask. See the information below on earguards and over-the-head ties or elastic to improve this aspect of your mask.

A note on edge leakAir that goes around the edge of the mask, whether inward or outward, is completely unfiltered. This means that respiratory particles in that air can travel from a person to the environment (air and surfaces); and from the air to a person. This edge leak reduces how good the mask is at filtering particles, the overall efficiency of the mask. We try to minimize edge leak by addressing breathability and fit.

​We discuss breathability in more detail on our home page and polypropylene in detail here. Polypropylene sellers can be found here.

​Other fit issues are covered on this page. This guidance is based on the peer-reviewed evidence and the opinion of mask researchers, mask designers and textile experts.

​Four studies demonstrate that attention to fit can improve the overall filtration of the mask.

  1. A peer-reviewed study on disposable masks, in which a mask with ties provided better filtration in an inward direction (i.e., protection of the wearer) than a similar mask on earloops. Experiments were conducted on one person.

  2. A peer-reviewed study on disposable and cloth masks, in which a number of mask modifications each provided better filtration in an inward direction. Experiments were conducted on one person.

  3. A peer-reviewed study on improving fit of cloth face covering with taping and with nylon hosiery. Experiments were conducted on manikins.

  4. A CDC report showing that knotting the earloop very close to the mask and tucking in the fabric provides better filtration in both inward and outward directions. Experiments were conducted using manikins and disposable masks (see below for our thoughts on how to apply this to cloth masks). The same CDC report showed that wearing a cloth mask over a disposable mask provides better filtration in both inward and outward directions. Experiments were conducted using manikins.

Double masking

Double masking has been shown to improve both the inward and outward filtration of masks. Experiments were conducted on manikins using a disposable mask underneath and a three-layer cloth mask as an outer layer.

There is an extensive previous literature on layering, summarized here. Double masking is essentially a method of layering and improving fit. We think that this advice can be applied to wearing two cloth masks.

Watch out for breathability, be sure you are comfortable in the double mask, and that the extra thickness is not making the leak around the edge actually worse. The aim is for most of each breath, in or out, to go through the material.

The experiments showed that a combination of cloth and polypropylene worked well. If your mask subjectively fits well, is breathable, and has at least one layer of non-woven industry-grade spunbond polypropylene​ as recommended by Health Canada, at is at least 3-layered, we think it is likely that you already have this advantage and do not need to double mask.

If you are unsure of the composition of your mask, it may improve the overall filtration to wear two masks.

Wash both masks after each use. Industry grade spunbond polypropylene can be hot washed but hang to dry - it will melt in a tumble dryer or if ironed.

If neither of your cloth masks is a pocket mask, and neither has polypropylene (or you are not sure if it has polypropylene), you can put a rectangle of washable polypropylene between the two masks, and the outer mask will hold it in place.

The CDC, Health Canada and the WHO recommend layering. 

Ear guards, hair clips, hats and headbands with buttons

In a peer-reviewed publication, hooking a disposable earloop mask onto an ear guard improved filtration in the inward direction. Experiments were conducted on one person. We think that ear guards, and buttons or hooks attached to a hat, head-band or head-covering are all ways of increasing the tension in the straps. Some methods also change the angle of the straps. We think that both these effects are likely improving filtration because they are reducing edge leak and improving fit to the sides of the face. We think that this idea can be applied to wearing cloth masks in the community.

Ear guards are strips of material with buttons or hooks at either end. They can be elastic or fixed length. They are widely commercially available, or can be made or improvised.

This may also be a useful modification for people wearing religious head-coverings or head-coverings for work.

Anecdotally, some people who wear earloop masks for extended periods find the use of ear guards improves comfort and reduces the need for adjustment. Others prefer to have nothing that interferes with their hair or head covering.

 

Mask fitter or mask brace

A mask fitter or mask brace is a washable outer structure that:

  1. Compresses the mask around its edges

  2. Provides two-to- four additional fixation points around the edge, which likely also improves fit

An improvised mask brace made of rubber bands (elastic bands) improved fit in a peer reviewed study of inward filtration. Tests were conducted on one person.

A template for a DIY mask brace to be made from a rubber sheet, and a link to a video tutorial, are available at Fix the Mask. Commercial products in a variety of different designs are also available.

The CDC recommends mask fitters or braces as a method of improving the filtration properties of masks by reducing leak.

 

The mask should fit snugly, without gaping, at the sides: consider knot-and-tuck for earloops

Many designs naturally lie flat or in a curved shape over the cheeks. In the Health Canada design, material is gathered onto the elastic at either side: anecdotally, we have found that it is important, as recommended by Health Canada, to stitch the material to the elastic to maintain the gathering, which is what gives curvature to the mask in this design.

In experiments performed only with disposable masks, tying the earloops in a knot close to the mask and folding in the excess material results in better filtration, presumably because of less edge leak. A short video explaining how to do this has been produced by the authors. They emphasize that it is important to make the knot as close to the mask as possible. Using this modification was associated with increased filtration, likely because of better fit, in a peer-reviewed publication showing increased filtration for the wearer, on a single individual, and in work conducted by the CDC on manikins, showing increased inward and outward protection. Both studies used disposable masks.

We don’t know whether knot-and-tuck applies to cloth masks.  If you have a mask that tends to gape at the sides, it is worth trying. However cloth masks are thicker than disposables, particularly at the edges, because of seams. If the knot-and-tuck method results is a lot of bulk at the edge of the mask, it may worsen, rather than improve, the fit.

If you are a mask maker designing a mask, consider that you do not have to attach the earloops to the corners of the mask, they can be closer together if that produces a better, flatter, fit.

Knot-and-tuck is recommended by the CDC for community masks.

​At the top of the mask, use a nose wire

A nose wire improved the filtration of a cloth mask in tests of inward filtration, protecting the wearer. 

Purpose-made flat bendable nose wires are now available commercially. Alternatives are plastic twist ties (use two), florist's wire, electrician's wire, or paper fasteners. Coffee clips are double twist ties, they tend to be wider, longer, and stronger and they work well in some designs. Pipe cleaners (chenille stems) can be used but tend to crumple when machine washed. Some masks are designed to allow the nose wire to be replaced if it breaks.

The metal nose wire make a moldable section for the bridge of the nose. This improves fit at the top of the mask by holding it in a contour that fits to the face, resisting the tendency for it to pull flat and tent over the nose. The wearer should take time to adjust the nose wire before wearing.

The nose wire also helps to reduce fogging of glasses by minimizing the leak across the top edge of the mask. We haven't found a good way to eliminate fogging completely.

Using a nose wire is recommended by the CDC.

Nylon hosiery (stockings, tights, pantyhose)

In peer-reviewed publications, a nylon sleeve was shown to reduce leak and improve filtration for cloth masks and for disposable masks. This modification tends to push mask material into the mouth (see below), unless the mask is quite strongly structured.

 

Adjustable earloops and adjustable over-the-head elastic or ties

A peer reviewed publication showed that, compared with earloops, over-the-head ties were associated with better overall filtration, presumably because of better fit. Research was conducted using disposable masks on one man and one woman.

 

Over-the-head elastic is likely to be similar to over-the-head ties, provided the tension is adjustable. Earloops with adjustment beads are commercially available. Pony beads or rainbow-loom elastics can be added to earloops to make them adjustable. Don't use anything that can become detached from the mask for younger children, because of the choking hazard.

 

​The mask should cover the wearer's nose and mouth at all times

The mask must be long enough to sit at least half way up the nose and extend to underneath the chin. Some designs of mask, like pleated masks, and Olson masks, curve naturally to fit under the chin. Other designs use a 3D structure or a duckbill structure to achieve this fit. If your mask isn't curving enough, it is possible that a small dart or tuck sewn in place in the centre of the mask may improve fit in this area.​

The mask shouldn't pull down or pull off the nose when talking

When we talk, the movement of the chin puts pressure on the bottom of the mask. The mask should be large enough that this shouldn't pull the mask off the nose. Respiratory particles are emitted from both nose and mouth, it is essential that both be covered at all times. 

The mask should be a suitable size for the wearer

We think the mask should extend at least an inch, and possibly more beyond the sides of the mouth. Masks that are wider rather than narrower offer the advantage of fitting a larger range of people, provided the fastenings are adjustable.

 

The mask should not require frequent adjustment

If it is slipping, the mask may be:

  1. too short for the wearer (top to bottom)

  2. too loose for the wearer (side to side)

  3. a bad fit for the particular wearer's face for some other reason

 

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Important special considerations apply to children

  1. For smaller children, buy or make a scaled down mask that fits their smaller face

  2. Other fit issues are the same as for adults

  3. Because children may be less tolerant of discomfort, it is even more important that the mask fits well and is comfortable.

  4. Don't use anything that can become detached from the mask for younger children, because of the choking hazard.

Knit fabrics should not be able to stretch over the nose and mouth

Knit fabrics are comfortable and popular with mask makers. Because they stretch, they offer the possibility of making the whole mask, including the earloops, from a single piece of material. We recommend that masks that use knits have stitching, edging, or incorporate a non-stretching material (such as polypropylene) that prevents the filtration surface from stretching when worn. This is the area over the nose and mouth, where filtration occurs. Stretching this portion of the filtration surface will open up the holes and reduce the ability of the material to trap particles. A home-made mask, made from T-shirt material, with edge stitching, provided useful levels of filtration in tests of inward and outward protection (reduction of particles reaching the wearer and the environment, respectively).

Ideally, the mask should not touch the mouth or pull in towards the mouth when breathing in

Not all masks meet this criterion: we think that masks which do touch the mouth are very likely still useful, especially if they are multi-layer masks, or can be used with double masking.

Our concern is that the mask fabric, which is acting as a filter for particles, may contaminate the mouth. We don’t know how important this issue is in practice. The solution is to choose a different design of mask, but we recognize that many people have already purchased masks. If you are a mask maker, incorporating a middle layer of polypropylene may give the mask enough structure to keep it away from the mouth. If your mask is a pocket mask, adding a rectangle of polypropylene may help in the same way.

 

Taping masks to the face

Using medical tape to tape the mask to the face has been shown to reduce leak. Anecdotally, some people who wear masks for extended periods have taped the top of mask to reduce glasses fogging or to reduce the need for adjustment. However, using tape on the face can cause bruising and skin damage when removed. We do not recommend this for community use.