I’ve done this - link HERE. I found the easiest way was like knacki said- mask and extract.
- Mask the area your face mask will be covering.
- Use Extract to create a “layer” around your original mesh. NOTE: this was the hardest part because I needed it to be tight around my face/head. The measurement on this tool is a little weird so I made a millimeter ruler in another app and imported it. I then used the ruler to measure how this the extracted layer was and undid/adjusted until I got it right.
- Subtract the extracted layer from my sculpted mask.
Make sure to have the Closing Action on to Fill or Shell (shell worked best for me).
