What Makes One Mask Better Than The Other?

All N95 masks and KN95 masks filter roughly the same.  Filtration, however, is only one aspect of a good mask.  If the mask does not seal properly to the face, the effectiveness of the mask reduces dramatically.  Critical environments where masks with perfect facial seal are required usually are accompanied with a professional fit test to ensure no leaks are present. There are three masks, in particular, designed to improve the ability to seal to the face without a fit test: SoftSeal, Envo and the 3M Elastomeric mask. 

Much has been written on how to find a better mask.  One such article was published by the Boston Globe.

To get a good seal against your face, there are three factors you should consider: 

1. Select a mask that is the correct size for your face. One size does NOT fit all faces.  The mask should fit between the bridge of your nose to just below your chin.  Many manufacturers only produce N95 masks in one size. Look for masks that come in several sizes so you can get one that is more specific for the length of your face.
2. The straps that go around your head have an important role in controlling how tight the mask seals to your face. Look for masks that have tension adjustments on the head straps so that you can get a tight seal. The straps on some masks lose their elasticity over time and since people are wearing N95 masks for longer periods, these adjustment features can compensate for changes in elasticity. Wider straps will also be more comfortable.
3. The material that interfaces to the face should be flexible to allow jaw movement and not break the seal and also should be comfortable to wear for extended periods of time.  Masks, such as CPAP masks for sleep apnea, that are designed to wear for long periods of time while maintaining a seal commonly use silicone as the material in the seal.  There are N95 masks available that use silicone as the seal material.