We are making masks for the current emergency. Note: This is not a CDC certified mask but it has extra filtering and it's what we've got for now. First off the pattern is a copy taken from an online source, craftpassion.com - and I've altered it a teeny bit by making the side edges of the lining shorter by 1/2 inch. I've altered the instructions considerably to fit my own technique for construction. I'll try to keep the instructions in line with the photos.
First thing to do is preshrink your 100% cotton fabric. If you have non woven fusible interfacing now's the time to use it. It is not necessary to use the same fabric for the lining and main pieces. Function is the purpose here. You'll need 1/8 - 1/4 inch flat elastic. I used 1/4 inch and it worked fine.
#1 Print the pattern - it will fit on a regular letter size sheet of paper. You will have to print it from the craftpassion.com website.
#2 After preshrinking and fusing the interfacing, cut the pattern. Remember to fold the fabric in half so that you end up with two pieces
that mirror each other - otherwise you get two identical pieces with no
matching opposite. I did this. It was exasperating! ***Note: In using the masks we are trying to prevent droplets, not air, from passing through the masks so perhaps in view of that info and in the interest of efficiency in the use of non woven fusible interfacing, one should only face either the main piece or the lining piece of the mask rather than both. 
#3 You will need these two feet. A regular foot and a zipper foot.
#4 Right sides together sew the curved edge of the two mirrored pieces of both the main fabric and the lining.
#5 Turn the side edges in 1/8 inch and sew in place.
#6 Right sides together (lining facing main piece) sew the curved top edges together. I used a 1/4 inch seam allowance. Go slowly around the curve so you get a nice hollow once it's turned right side out. You'll have to ease it upward with your left hand as you go.
#7 I used a light weight wire about 4 inches long for the nose piece -
about 14 gauge - turn the ends up and inward. *****The online video asks for
cuttings from an aluminum pan. I didn't do that. If you don't have wire you
can use a couple twist ties wound around each other but wire works best.
#9 Bend the wire into a curve that matches the curve in the pattern, doesn't have to be exact - the point is to be able to stitch around the bend, you'll be able to shape it to your nose when you've finished. Tuck it into place inside the mask approximating the center to the center of the pattern.
#10 Switch to the zipper foot and move the needle to the right outer edge of the foot. Your right!
#11 On the outside of the mask begin sewing 1/8 - 1/4 " from one edge along the top like a top stitch. I started at 1/8 and then as I approached the wired piece I expanded to 1/4". You have to hold the wire in place with your right fingers/nails and go slow, this is where needle breakage comes in. Grrrr...I hate when that happens!
As you approach the wire, stop and back stitch at a slant to the top edge to form a stop line of stitching to keep the wire from moving. Go forward repeating the slant so you have a re-inforced row of stitching and then continue following the curve of the pattern with the wire inside. Go slowly. When you reach the end of the wire do a slant up to the upper edge like you did at the beginning of the wire and then backstitch down to form the other stop line. Then continue to the end of the pattern piece.
#12 This shows the direction of the stitching. After you've done it a couple times it will be easier. You'll get the knack of it. It's not going to be a vision of perfection unless of course you are a perfectionist. Remember, the purpose of the mask is function.
#13 Turn the mask inside out. You will now sew the bottom edge together - be sure to match the center seams. Note that the outer main edges do not meet with the inner lining edges.
#14 Sew across the bottom edge from the outer edge of the main fabric all the way to the other outer edge of the main fabric.
#15 Turn the mask right side out.
#16 Lay it flat and finger press or iron the outer edges so that they are even right up to the stitching - use a pointy thing or a pencil inside to push the edges out...know what I mean?
#17 Stitch across the bottom edge.
#18 This is a bit tricky. Fold the outer edge of the main/front of the mask over the elastic and back onto the inside. Here's where you have to be careful not to catch the elastic in the stitching because you want the elastic to be able to slide in its sleeve. Sew a line very close to the edge following the folded over line of stitching - you can sew right on top of that stitching. Hold the elastic back with your fingernails as you sew and go slowly.
*****Use a knotting stitch at the beginning or do a couple backstitches to secure the beginning of the seam. It helps to start the seam about 1/4 inch or so past the outer edge and then backstitch because the fat seam at the beginning gets caught in the presser foot and you can break a needle! God forbid! So again, go slowly.
#19 When you get to the end do a few backstitches or a knotting stitch. Sorry for the fuzzy photo...
#20 Bring the elastic around to the other side and make sure there are
no twists in it. Then repeat the procedure making a second sleeve to secure the elastic in the
other side.**** The elastic should be approximately 26-28" long for an adult. 22-24" for a child.
#21 Pin the two ends together with a safety pin and try on the mask. Don't use a straight pin or it will skewer you in the head. Once you've determined the length you need, sew the two pieces of elastic together - be sure they are not twisted.
#22 Fit the nosepiece by bending the wire to the shape of your own exceptional proboscis and - Voila!!! You have a mask!
***I don't know who this strange lady is...she volunteered...
