We'll make a two-layer mask with elastic bands on the edges that slide over your ears.
It's not hard to find materials around your house that will work perfectly for your mask, even if you don't have a giant closet full of fabric. I used a workout towel for the liner layer, and a t-shirt sleeve for the front of the mask.
The important thing is to use fabric that breathes and doesn't fray much on the edges -- cotton or other natural fibers are your friend here. Hold it up to your face and try breathing through it before making your final decision.
And, use tightly-woven cotton fabric on both sides - so no gauzes.
If you're not sure what a fabric is made of, try a burn test -- pull out one thread and carefully catch it on fire with a lighter. If it burns up to ash, you've got natural fibers. If it melts, it's a polyester-type manmade material.
This pattern is based on a pattern posted by CraftPassion.com.
Once you've downloaded, print out two copies.
Place the plastic window pattern piece onto your clear plastic cup. Place it closer to the top for larger sizes or closer to the bottom for kid sizes. Cut the oval of plastic out with scissors.
Get your anti-fog gel and squeeze a bit on the inside of the window. Read the directions for use -- but for most of these, the directions boil down to "rub it in vigorously with your finger, then rinse it off immediately.". Let it air dry.
Lay one pattern piece face up and one piece face down on your lining fabric. Leave a little space between the pieces. Trace around them with a marker, then draw another line 1/4" away from your first line. This is our seam allowance -- we'll trim it down a bit later, but it's there to give us a little more room to work.
Cut out the shapes and clip the seam allowance to the pattern line at the deepest point of the mouth hole. Fold the top and bottom seam allowance sections down to make a narrow hem around the opening. Glue the seams and place something heavy on top until they're dry. You don't need to wait the full 24 hours -- I found that around 20 minutes of dry time would give me a good hold.
Stack your two lining pieces with right sides together (so the glued seam allowances are on the outside top and bottom).
Glue the front top and bottom edges of the two pieces together to make the front seam. Don't glue the mouth hole edges together! Just the part that will go over your nose and over your chin.
Place something heavy on top and let this seam dry.
I'm using a t-shirt sleeve for my mask, so I started by cutting the sleeve off the t-shirt, then cut along the underarm seam so I had a nice flat piece of fabric.
Think about how you want your mask pattern to lay out on your face, and line the pattern pieces up with the design on your fabric before you cut.
Trace your seam allowance lines 1/4" outside your pattern lines, just like you did with the lining.
Cut out the pattern pieces on the seam allowance line. You can make a narrow hem around the mouth the same way you did for the lining, or, if your fabric doesn't ravel at the edges, you can just neatly trim off the seam allowance and leave the edges raw. With some fabrics this will give a cleaner, sleeker look to the outside of your mask.
Stack the two pieces, right-sides-together again (so the pattern is on the inside and you're looking at the back of the fabric). Glue the front edge at the top and bottom, again leaving the mouth hole open.
Once the center seam has dried, open up the mask and lay it as flat as you can. Put some glue around the edge of the window, being careful not to get glue in the middle of the window. (If you do get some out-of-place, you can remove it with 99% alcohol). Be generous with the glue. We want to make a fairly airtight seal all the way around.
Flip it over and be sure everything looks nice and even from the front side. Let it dry.
Place your lining face up on the table, and place the front of the mask face down on top of it (right sides together, so the seams are on the outside).
Glue across the top edge and the bottom edge, leaving the sides open. Let these seams dry.
Turn your mask right-side out. Fold the edges in so they look neat and tidy. You can press the with an iron if you'd like -- just be sure not to iron your plastic window or it will melt.
Slip your elastic band in between the front and back pieces on the sides. It doesn't need to go all the way to the top and bottom of the edges -- adjust it so it fits your face. Glue the edges down.
Since this is a stress point, I didn't want to trust the glue entirely to keep the ear pieces in place, so I reinforced the glued edges with three staples on each side. The staples sink nicely into the towel fabric so they don't irritate my face.
Let your mask dry in the sunshine for at least 48 hours before you wear it. Let the glue fully cure and air out until you can't smell the glue anymore when you put the mask on.
You can wash this mask -- and you should wash it often -- but don't put it in the dryer or you'll risk melting the plastic and breaking down the glue.
After washing, re-apply your anti-fog gel to the inside of your window and give a rinse before you let the mask air-dry.