Design & Features

Design FAQ

Q. Where can I get the STL files and CAD files for the latest version?

A. STL files for the latest version can be found here. CAD files for the latest version can be found here.

Q. How many designs are available?

A. Our team has released one major design (Version 1) with testing information using replaceable polypropylene MERV15 filter material. Our design is regularly being updated with improvements. Please check our Iterations summary below for details. It is recommended to use the latest version available.

Q. Can I change the mask design files?

A. With open source designs, we encourage local innovation with attribution. We hope you will share your improvements and keep us posted. Our research and tests are based on the design files we provide, so please remember that changes to the design may warrant new tests. For more on our pre-NIOSH testing process, please review our Testing and Validation information.

Q. Can I customize the fit of the mask?

A. Unlike standard N95 masks which come in limited sizes, the BE mask comes in a variety of sizes to fit more faces. Select the correct size based on the Fitting Guide. If you need to modify the shape and fit for unique individuals, the files can be scaled in relation to the X, Y, and Z dimensions. Keep in mind that the filter component will be scaled in relation to the whole model. We have conducted research on the sizes of masks along with common facial geometries which may support your customization process.  

Q. Can I suggest or add improvements?

A. Yes! Use the BE Hub space to share your experiences and suggestions. We will be pleased to respond and will consider including any improvements made by the community in future iterations of the BE mask.

The BE mask is offered to the general public for general, non-medical purposes. In accord with FDA Emergency Use Authorization, it has been submitted for review to NIOSH. The safety and efficacy of any mask depends on fitting, sanitization practices, and filter materials. Any mask should be tested and fit to meet local needs and standards. Please see our user liability disclaimer for details.


The BE Mask is derived from the Montana Mask. It incorporates improvements to materials, fit, assembly process, seal, structure, sizing, and filter cartridge design based on our observations through testing.

Montana MaskBE Mask 1.3.4
Mask Frame MaterialPLA recommendedTPU recommended
Sizing2 sizes (S – L)
Custom scaling
3 sizes (S-M-L)
Custom scaling
Mask Front GridThinner protective gridThicker protective grid
Added fillets (printing support)
Mask WallsThicker mask wallsThinner mask walls (flexible)
EyeletsEdge of maskRemodeled (away from eyes)
Filter TestingTesting with cut up N95 mask
(6 filters)
Polypropylene MERV15 
(single use, 2-ply)



The mask has been modified to move the top strap points away from the mask edge to make room for gasket material; a cage structure was added to the front of the mask to maintain filter material integrity; the mask depth was extended to provide more clearance between face and filter; three mask sizes were created:

Small, Medium, and Large (size is equivalent to original Montana Mask)

See the sizing guide at the end of the document to help in selecting a size.

Filter Frame

The filter frame component has an added flange to ensure it is not inserted too far and to provide an extra barrier around the edges of the filter.

Filter Material 

The filter material we have been using is MERV 15 polypropylene plastic filter taken from bag air filters. We identified this material because it has a high filtration performance rating and can be readily sourced from an industrial supplier. 

Other suggested filter material supply chains appear overwhelmed. Our source:

This is the specific version we have been using:

The original Montana Mask site also points to a specific resource for filter materials – Flowmark/Hightech. However, due to overwhelming demand for their filter material, they messaged on their website that as of 4/2/20 they will only supply healthcare facilities.

We recommend layering the filter with double ply sections of MERV 15


We are using a silicone foam rubber material with a C-channel opening to be placed around the edge of the mask to ensure a tighter fit and reduce leakage. The dimensions are shown in the image. Our source:

See our video tutorial for installing the lining on the mask here:


We currently do not have a standard strap to recommend. Our group is using various materials and methods of securing. Ideally, a material that can be easily cleaned or replaced should be used. A few options:

  • Elastic strap (¼” elastic strap material is available through eBay: ‘Flat Braided Elastic Cord~Knit Elastic 1/4” Width~Trim Ear Hanging Sewing’).

  • If that particular seller runs out of inventory, you can search eBay for other sellers of ¼” elastic. A single piece of ¼” elastic about 38 inches long combined with a barrel lock is an effective solution. See images on the right.

  • Rubber bands that can be “daisy-chained” to find a proper length. (You can source these anywhere but as a reference for size we have tried ¼” wide, 3 ½” long rubber bands from McMaster-Carr. The image on the right (orange bands) shows this solution with zip ties used to anchor the rubber bands since they do not fit through the holes.

  • Shoelaces or similar cord material that can be tied or held in place with a cord lock.


BE Mask 1.0 (BECMv1)

Our first public release, the BECMv1 Crisis Mask has undergone the most testing to meet immediate needs.  

  • Available in 6 sizes (xxs – xs – s – m – l – xl).
  • Design Features
    • Design supports semi flex TPU material without needing gasketing materials
    • Adjusted eyelets to support a wider range of materials
    • Scaling of components has been adjusted to improve seal 
    • Size series to improve fit comfort, minimize leakage, and improve safety.
    • Interlocking filter lattice for layered protection of 2-ply MERV15 filter
  • Download files here

BE Mask 1.3.4

With community feedback, we have made improvements 

  • Available in three sizes (s – m – l ).
  • Design Features
    • Versioning and size indicators included 
    • Walls thinner, lighter weight
    • Eyelets repositioned and enlarged
    • Adjust shape for better fit around nose
  • Download files here

Version Comparison

BE Mask 1.0BE Mask 1.3.4
Sizing6 sizes (XXS-XS-S-M-L-XL)
Custom scaling
3 sizes (S-M-L)
Custom scaling
Mask BodyModified mesh files
Based on Montana Mask
Solid-body models
Mask Front GridThinner protective gridThicker protective grid
Added fillets (printing support)
Mask WallsThicker mask wallsThinner mask walls (more flexible)
Close to edge
Repositioned and remodeled
Version Number NoIncluded on mask body interior
Sizing IndicatorNoIncluded on mask body 
Included on filter frame insert