How to build a PAPRa Mask (Aug 2021 Version)

The Tetra Powered Air Purified Respirator requires a Mask component to deliver purified air to the face of the wearer. This mask will be connected to the Fan Box via a CPAP hose. In our testing of the mask, it has been comfortable to wear for several hours, and provides protection while the device is powered on. When the device is powered off, the mask is not effective, and so we are still iterating on the mask design to provide protection when the device is powered off. A single battery charge can provide up to 4 hours of protection, which is sufficient for many use cases for us to feel comfortable publishing this mask.

WARNING: we provide no warranty, implicit or explicit, that this device will work up to an N95 specification, when built outside of a facility rated to do so. The only way to truly test one of these devices using something like a Portacount under controlled conditions.

This photo shows all the parts laid out for building this component:

Note that this build includes three different sizes of mask body, but only one body is needed for the final build. Each one is based on the NIOSH head forms for small, medium, and large, respectively.

The assembly diagram can be found here.

You will need these components. Prices fluctuate, and so are not included here. Alternative versions can be sourced, and we welcome edits for tested alternatives.

These tools are recommended. URLs are for tools purchased and used in the building of the prototypes:

While the respirator body has changed somewhat since these instructions were first written, the instructions below remain correct for these newer parts.

Once the mask has been printed, the build consists mainly of getting the 3-ply Medical Face Mask material onto the mask so that the wearer’s exhalations can exit the mask without affecting those around them.

Cut the side supports of the surgical mask off so the accordion folds can be unfolded:

Draw a circle on the mask where you want to cut out the filter material (You might be able to get two filters from one mask):

Cut out the filter material:

Place the circular gasket into the cap:

Place the filter material over the gasket and cap:

Fold the mask so you can place the Mount over the nose portion of the mask:

Seat the mask over the filter material in the cap:

Clip all of the clips to hold the filter in place:

Cut a hole in the bottom of the mask for the grommet (note-- if you just want a passive respirator, no need to do this step!):

Force the grommet through the hole, taking care to rotate the grommet so airflow goes away from the face:

Push the bathing suit elastic through the attachment points on the mask as one long strand. Some prefer to tie at the top of the head, while others may prefer behind the neck. Note how the elastic emerges from behind the attachment points to wrap around the head and neck:

Congratulations! You now have a TETRA PAPRa face mask v3!

Changing the filter depends on how much you use the device. If you’re using the device where there are a lot of particulates in the air (such as a construction site or a woodshop), you may want to change every few days or so. If you’re using the device where there are less particulates, every two to three weeks should be fine. If the filter material gets dirty or wet, you should change it. The blue layer is intended to be water proof, but we don’t know how much actual water it can take.

You can clean the hose with a 22mm cleaning brush (like https://www.amazon.com/JAKIA-CPAP-Brush-Cleaning-7inch/dp/B089Q6QH1X). Soap and water should be sufficient. We’ve found that the hose material can begin to smell if exposed to quite a bit of sunlight, such as wearing the PAPR in the desert, and this smell wears off after some time.