ADDING A NOSE WIRE TO THE MASK

In some cases, a nose wire is helpful -- people who wear glasses sometimes have problems with fogging lenses if the mask isn't snug around the bridge of their nose. 

I've found that the closure strips from coffee bags make great nose wires (specifically Peet's Coffee, although others might be similar). The strips are 5" long and 1/4" wide; I pulled the glue off the strip before using it in the mask.

 
These instructions are for a flat mask that is shaped by pleats. I don't know if this method would work on a mask with a curved center seam. You may be able to affix a bias strip at the bridge of a curved mask and insert one of these strips into it, but I have not tried that.

First, the outside of the finished mask showing the curve of the nose wire at the top of the mask:

 

Next, a photo of the inside, showing the placement and stitching of the strip:

After you've turned the mask inside right and pressed it (step 6 in the original tutorial), edge stitch across the top of the mask, about 1/8" in from the edge. Lock your stitch line at either end. Then slide the bag closure strip inside the mask through the opening at the bottom of the mask. It can be a little difficult to get the strip in place, but it should be centered at the top of the mask as much as possible, and on the outer side of the seam allowances to give a little extra cushioning for the nose.

When you have the strip in place, put a pin at either end to keep it from shifting and also put pins along the length of it to keep it against the upper edge of the mask. You'll need to remove the pins as you sew around the strip, so be sure to insert them so you can pull them out as you go along. Switch to the zipper foot for your machine and do an outline stitch to keep the strip in place. Backstitch across both ends of the strip to make sure it won't shift out of place.

After you have the nose strip sewn in place, proceed to step 7 of the original tutorial -- making the side pleats. From here on, follow the original tutorial, with the exception of the final edge stitching. Because you edge stitched across the top edge before inserting the nose strip, there's no need to re-stitch along that edge. Instead, start your final edge stitch at the top left corner, stitch down the side, then across the bottom and the center pleat, and up the other side. Be sure to reinforce all the corners with backstitching and to triple stitch the pleat, as shown in the original tutorial. 

I've had no problem with the strips getting damaged or permanently distorted in the wash. I put the masks in a lingerie bag and put them in the wash machine with a small load of laundry that I wash on gentle cycle. They go in the dryer loose and get tumbled along with the rest of the laundry load. They are a bit rumpled when they finish drying, but they smooth out easily.