There have been many “hacks” and tricks for preventing glasses from fogging, but the only way I’ve found that really works is sewing or taping in a flap. Here are the sewing instructions. If you want to do this for a disposable mask, just use some tape and a sturdy paper towel to do the same thing.
To do this project, you will need about 6-7 cm. anodized aluminum wire of about 2 mm. thickness. This is the sort usually used for floral arrangements and sometimes to make hypoallergenic jewelry. The reason I like this is that it can be easily curled up at the ends so you don’t poke yourself. It is also soft enough to truly form fit your face, but not so rigid that it is uncomfortable.
You will also need a length of soft ribbon, bias tape, or fabric that will be wide enough for room to cover the wire and fill in any gaps between the mask and your face. This is what will be blocking the air flow upwards so that your breath doesn’t reach your glasses to fog them up.
Just sew the ribbon over the wire. I like to do a sort of overhand stitch first, and then go back and do a neater blanket stitch.
Then just adjust the mask around your nose, and flip the flap up before you put it on again.
As I mentioned before, if you’re using a disposable mask, you can make a flap with a paper towel and some wide medical tape.
If you have any other tips, feel free to comment.