Advice on Getting the Best Fit
An example of a well-fitting mask. This 3D mask has structure which gives it volume and allows mouth movement, and it fits snugly on either side of the nose, at the sides and under the chin.
N95s achieve great fit through structure, nosewires and overhead elastic. Read about the whole range of mask types here and find N95s here.
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 bottom centre of the mask may improve fit in this area. Alternatively, you may need a mask that is longer top-to-bottom.
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 long enough, top-to-bottom, that opening the mouth wide 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 problems may be:
the mask is too short for the wearer (top to bottom)
the mask is too loose for the wearer (side to side)
the head attachments are the wrong size or not adjusted properly
the mask is a bad fit for the particular wearer's face for some other reason
Ideally, the mask should not touch the mouth when talking
This is uncomfortable and annoying. Anecdotally, 3D designs minimize this problem. 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.
We don’t know, however, if it is an important issue either for protection of the wearer or for source control.
We summarize the evidence around fit issues here.