Mask lanyards are more specific than regular lanyards. They have two lobster claw clasps, one on each end, and sit around the neck similar to the hangers used for eyeglasses.

They are a little shorter than regular lanyards. This is so that your mask isn't dragging through things when you bend over. Mask lanyards help keep your mask handy for when you are in situations where you need to place and remove it often, eg: in and out of the car, stores etc. Just clip an end on to each ear strap and you are all set.

I make them in  the same way as regular lanyards with the exception of the ends and length. To start off, I cut then fold the fabric over in half length-wise and iron it. I do the same again this time folding each side over towards the middle crease. One final fold over, folding it in half length-wise once again and ironing it flat again. I then sew down the length on both sides closing the folds down.

I attach a lobster claw clasp to each end, fold over, and sew the ends up, going back and forth several times. 

The fabric used is 100% cotton. They are 100% homemade, and make great small gifts.
Each adult size lanyard is approximately approximately 28 inches not including the clasps.

Unwashed, but it machine washable/dryable. 
When I sell the lanyards, the mask in the photographs are not included.