Introduction: Make 4 N95 Filters From Each N95 Mask (3D Printed)

At this time, the N95 masks are precious. The goal of the BaileyMask is to make 4 filters (33mm x 75mm) from each full N95 mask.

It has a tight seal around the face, and a check valve system to reduce humidity inside the mask and thereby extend the usefulness of the filter. The filter can be removed and sterilized with UV and hydrogen peroxide. The filter box can be easily adjusted so air freely bypasses the filter when full protection is not needed.

This build requires a 3D printer. STL files are included. I will add the SAT, X3D files soon.

DISCLAIMER: I am not a medical engineer. Although I have tested this for myself, I can't promise it will work for you. Please don't suffocate yourself or your friends, or expose anyone to Coronavirus.

Please be sure that you follow these basic principles:

1) The filter must be N95. Anything less won't protect you
2) The filter must fit perfectly into the filter box and seal all the way around. 33mm x 75mm
3) The filter box must have a gasket (rubber band) and be held tightly to the mask.
4) Please be sure the mask seals tightly to your face. If not you will suck unfiltered air.
5) The straps should be elastic AND adjustable (Velcro). Required for a good fit and comfort.


1 - 3D printer and 75g of filament (I'm using PLA) to create 3 pieces. ~3.5 hours at lowest quality.

1 - N95 Respirator mask (can cut 4 filters 33mm x75mm)

1.5mm thick foam craft material for check valves
a) Inhale: 37mm x 31mm
b) Exhale: 39mm x 5mm

Thin Yoga mat or other rubbery membrane to make a seal to your face.

Flexible adhesive to hold the Face-gasket to the mask, and create a hinges for the check valves. I like ShooGoo.

Materials for making straps: Elastic, Velcro, string, needle and thread.

Cutting tools for the gasket and check valves.

The 3D Files:
The intent is that these files can be printed without any support to reduce the time to print. It just barely makes it around some parts.

Step 1: Installing the N95 Filter Into the Filter Box

The filter-box and filter-screen are designed to securely hold a piece of N95 filter cut exactly 33mm x 75mm. Any larger or smaller in either dimension will result in a poor fit that might result in air passing by the filter and exposing you to contaminants (including corona-virus).

I like to use different colors for the box and screen so you visually confirm the seal around the filter.

It's also important to note that the filter-screen will only fit in one direction. The corners are rounded on the top, but square on the bottom.

Step 2: Installing the Filter Box

Having the filter box separate from the face mask provides flexibility in design, and provides a bypass mechanism:

The filter Box fits into the mask frame and seals tight with a rubber gasket. It's held in place by a rubber band.

This design allows the wearer to adjust the filter box to allow air to bypass the filter when full protection is not needed, e.g. walking from your car to the store.

Step 3: Marking, Cutting, and Gluing the Face-gasket

The "Face-gasket" is a critical component of the BaileyMask. It provides a seal around your mouth and nose to assure all air passes through the filter material on the inhale. The inside profile of the gasket can be custom cut to conform to most faces.

I am using a thin yoga mat. You could also use the 3mm thick craft foam board, or anything that will be flexible enough to conform to your face.

3 steps:
1) Mark the outside of the gasket material, and cut out a blank.
2) Mark the inside perimeter of the gasket to suit your face
3) Cut the inside of the gasket and glue to the 3D printed mask.

I included the STL file for the gasket jig here, but it was a 6-hour print. If you are only making one or two, this is not necessary. You can just rock the mask back and fourth on a flat surface.

Step 4: Create Check-valves: Inhale and Exhale

The check-valves force the inhale to go through the primary filter. The exhale goes through the smaller filter at the bottom.This keeps the primary filter dryer.

I have used a variety of materials for these flaps; I like the thin foam sheet material best. It's easy to work with and it provides a good seal.


For the small exhale check flap, it's very important that it doesn't fit too tight. glue at just one end.

For the larger Inhale flap, it's important that it not be larger than the box... it would hit on the mask and not open (this would be the suffocation part I warned about at the beginning).

Step 5: Making Straps

It's important to keep this secured to your face. If air passes by on the inhale you are in danger. If air passes on the exhale, you are endangering others.

The mask part has 4 hooks for attaching straps. I used string, elastic, and Velcro.

Using Velcro makes it adjustable, but you really need the elastic too for securing it in place.

The bottom strap must be 'dis-connectable' so you can strap it around the back of your neck like a necklace.

You want something you can 'set-and-forget'. You don't want to be fidgeting with this think when you're out.

It must be 'secure'. you don't want a strap to break or come un-tied.

Step 6: Cutting the N95 Mask Into 4 Filters 75mm X 33mm

N95 Masks are in short supply. So don't start this step until you have printed your Mask, FilterBox, and FilterScreen. This will quadruple your supply of N95 filters.

1) Make a template out of paper-towel exactly 75mm x 33mm.

a) Test Fit your template into the FilterBox and capture with the FilterScreen

2) Lay the template on the mask and trace out rectangles. You should be able to fit 4 on one mask.

3) Use scissors to cut on your lines


1) Avoid the metal strap for the nose-pinch, and the spots where the straps are glued on.
2) Flatten the filter material out as you trace and cut.
3) Once cut, you fill find 3 distinct layers. Keep all three layers together in the right order.
4) Keep track of inside vs. outside. Be sure to install into the FilterBox in the proper orientation.