Mask FAQ’s: Using an HVAC Filter in a Face Mask

Please Note: We have provided answers to these questions to the best of our knowledge and according to released data; We do not make any guarantees, nor are we the final authority on the subject. Professional grade medical masks, such as N95s, would be the ideal mask to wear, but given the national shortage and need for N95 masks to be distributed to medical personnel, cloth masks with MERV-13 air filter inserts are a better option than to just to have a cloth mask. We hope these FAQs are helpful, but if you have further questions, feel free to email us at

Q: Do these filter inserts contain fiberglass?

A: To our knowledge and after speaking with a representative of the manufacturer, no. However, the processing equipment used to produce these filters also produces supplies that do contain fiberglass. With that being said, we cannot make a guarantee that it does not have any trace of fiberglass. To stay safe, each wearer should not breathe directly through the air filter, rather, they should breathe through the mask, with the air filter in between the fabric.

Q: On the filter material I received there is a small, hard spot that looks like dried glue…?

A: It is glue. We are dismantling high-efficiency filters from our stock to obtain the filtering material for the community. To do this, we have to remove the glued ribbons and metal screening that keep the filter’s shape when used in a home’s air stream. We have tried to remove all these small drops of glue, however a piece may have been missed. You can carefully remove the piece or just cut the mask so that the glue spot will not be directly in front of your mouth.

Q: Should you clean and sterilize the mask after each use?

A: Yes. After using the mask in public, the mask should be cleaned or sterilized. Caution should be taken in handling the mask after use, and you should avoid touching the front of it which may be contaminated.

Since there is no plastic used in the mask, heat can be used as a sterilization method. To sterilize the mask between each use, preheat an oven to 170°F. Place the mask with the filter material still inside it on a baking sheet within the hot oven for 30 minutes or more. Viruses and germs will typically not survive temperatures on surfaces at about 150°F. Setting your oven to 170°F ensures the mask gets hot enough in the event of oven variability. Source

If you need to wash the mask, remove the filter material and hand wash. Machine washing tends to crumple the nose wire which will cause it to eventually break. The mask can be air dried or dried in a clothes dryer if there are no other clothes in the dryer that would damage the wire.

Do not use a microwave since this will not kill viruses and the mask has metal in it.

Do not use a dryer to sterilize since dryers typically only heat up to 135°F.

Q: Is there a potential that the filter material will break down and I could potentially inhale the fibers?

A: Since the material we are supplying is being taken from a high-efficiency filter media designed for furnaces and air conditioners, they are typically installed in air streams where the air has a velocity of at least 1,000 feet per minute (fpm). The velocity of most people’s breathing is only about 200-400 fpm, so the filter breaking down should not be an issue. The fact that the cotton cloth is between you and the filter should also protect you should any pieces come loose from when the material was cut or placed into the mask.

Q: I’ve read that MERV-13 filter material can trap molecules between 0.3 – 1.0 microns, however, some article state that the virus can be smaller than that?

A: Although the virus itself is said to be about 1.25 microns, so far, its verified means of travel is as a droplet nuclei. A viral nuclei is composed of the virus which is surrounded by fatty proteins and mucus. This covering is what protects it outside of a host—sort like a space suit it needs to survive once it leaves a body. This is also why heat and UV affect it, because heat dries up the mucus and fatty proteins around it causing the virus to expire. Further increasing the size of this particle, is that when expelled from the body, the viral nuclei is contained within the vapor droplets from a sneeze or cough. The viral nuclei contained within the water vapor is what the MERV 13 filter material is rated as being able to filter. You can use a higher rated MERV filter in a pocket mask if you can obtain it, however it will be harder to breathe through.