The Fixation Masks by Shannon Dunbabin use Fixation, a stretchy cotton/elastic blend. Fixation I-cords make perfect ear straps! The elastic in Fixation helps to ensure a more secure fit.
The pattern is also available as a double layer which includes an opening to allow a filter. The pattern for the double layer is available here.
The masks are knit using size US 4 needles.
This pattern is available as a PDF download.