Polypropylene material filters for masks. Polypropylene is commonly used in various medical applications due to high chemical and bacterial resistance. Disposable syringes is the most common medical application of polypropylene. Other applications include medical vials, diagnostic devices, petri dishes, intravenous bottles, specimen bottles, food trays, pans, pill containers, etc. It is also one of the layers used in N95s.
I recommend using these if you're higher risk, live near an epicenter or have to go to the hospital.
They are being sold at my cost of $2.5/10 You can also try doubling them up for extra filtration!!
In view of the pandemic, having these filters for my masks gives an extra layer of protection.