One of the most effective materials you can use to prevent transmission of the 2019 coronavirus may be the lining used in furnace filters, which are engineered to purify air. Making one shouldn't take long, provided you have a few basic sewing supplies.
Please keep in mind these materials are precious—people confronting the disease directly need these kinds of defenses, so don't buy out your hardware store and hoard a bunch of filters. Limit home use of these masks to covering up when you or a member of your household is experiencing symptoms.
If you have time, resources, and some sewing know-how, you might even consider making and donating these masks to healthcare workers on the front lines of confronting COVID-19.
Safety note: The U.S. Centers for Disease Control recommend officially certified N95 masks for protection. Anything other than official equipment comes with no guarantees of safety or effectiveness.
Step 1 - Find a Filter
Check the labeling if you can. Some furnace filters are specifically designed to stop viruses. Whatever kind you have available, use a fresh, clean filter if possible. Using a used, dirty sheet might be dangerous.
Step 2 - Determine the Sides
If there's an arrow on one side of the material, that's the side to label as "inside."
Step 3 - Remove Cardboard and Wire
These heavier elements will get in your way and could cause discomfort or injury.
Step 4 - Measure and Cut
Divide the material into seven inch squares.
Step 5 - Add Structure
Sew a sturdy pipe cleaner or twist tie along the top edge.
Step 6 - Pleat Sides
Scrunch the sides down to four inches and pleat them in place so the center is the full seven and the sides are four.
Step 7 - Add Elastic
Cut two six inch pieces of elastic and sew two edges of the filter closed around them to make ear loops.