Silk is a textile with some interesting properties. It is considered hydrophobic compared to other textiles in that it repels and prevents absorption of droplets. It has good breathability and can be cleaned easily.
Alone, as a face mask, some studies have shown its ability to filter viral particles as relatively low. Silk was the lowest performer in one study filtering only 58% of particles measuring 1 micron, while cotton T-shirts ranged from 69% to 74% filtration depending on the composition of the T-shirt. These studies are difficult to broadly interpret as much of the filtration capabilities is also dependent on the tightness of the weave of the textile used in the study.
That being said, silk may serve a role as a second face mask or in a 2 ply or multiply face mask. Silk has been studied if, when treated with antimicrobials, can reduce inflammation in the skin including acne. Studies looking at how much bacteria colonizes silk compared to cotton for coliform bacteria (from the colon) have been unclear in that although some show bacteria are less likely to colonize silk compared to cotton, it is not certain if this is a property of the silk itself or other aspects to its production.