Cut out 4 mask pattern pieces (2 exterior, 2 liner).
Stitch front seam 1/4'' seam allowance (both sets).
Open up liner and exterior mask pieces:
Pin right sides together, matching front seams:
Stitch together 1/4'' seam allowance top and bottom only (leave sides open).
Turn inside out and press seams to edge.
Turn sides inside concealing raw edge about 3/8'' (does not need to be exact).
Cut about 6 inches of 1/4''-wide elastic and pin inside mask.
Fit mask to size:
Stitch around perimeter of mask 1/8'' from edge securing elastic and seams.
Stitch second stitch line 1/4'' from first stitch line for additional elastic security:
Snip any extra loose threads.