Badger Seal (Mask Fitter, Mask Sealer, Mask Brace)

What is the Badger Seal (mask fitter)? A soft, flexible and adjustable “frame” that significantly improves the outer seal of a mask.

Why use it? 

  • Increase filtration performance: Adding the Badger Seal to a 3-ply disposable mask reduces the effective particle penetration by typically 15x (see the Performance section below).
  • Breathability: Instead of wearing double masks, which can make it harder to breathe, the Badger Seal only needs a single 3-ply disposable mask.
  • Reduce fogging with eyeglasses: The sealing along your nose typically eliminates any fogging on eye glasses.
  • Reduce slipping: Keeps your mask from slipping down your nose by holding it in place while still flexing for jaw movement.

What makes the Badger Seal unique?

  • Cheap: < $1 in materials
  • Simple: Easy to assemble in small or large quantities using readily available materials and household tools.
  • Comfortable: The soft nosepiece forms to the custom 3D shape of your face. The elastic chin strap keeps the seal while allowing the jaw to move freely while talking. The elastic strap passes around the back of the head and can be adjusted for more or less pressure without straining the ears. Weighing only ~5 grams, it’s extremely light.
  • Easy to use: Once the Badger Seal is formed to your face and the elastic strap is knotted to maintain a comfortable pressure, it can be put on and taken off very quickly.
  • Open Source: The design details including how-to videos can be found here.

What type of mask should I use? The Badger Seal with a 3-ply disposable mask was shown to have great filtration performance while also being low-cost and made from a very breathable material (see the Performance section below). Significant improvements were also seen when the Badger Seal was worn with a 4-ply knit cotton cloth mask or an ASTM Level II mask. Since the outer edges will be much more sealed than usual, you must ensure your mask is made of a sufficiently breathable material.

How can I make a Badger Seal? Click here for the Open Source design including detailed steps, drawings and videos.

Warning: While our fitter seems to improve the seal of a face mask, it has not been tested for effectiveness in preventing illness, and you should use it at your own risk. See legal disclaimer at the bottom of this page.

Obtaining / Purchasing:

Option #1: Badger Seals can be purchased via external manufactures here and usually on eBay and Etsy (separate sites, not affiliated with UW-Madison).

Option #2: If you are part of UW-Madison, you can use ShopUW+ to order a Badger Seal(s) items free of charge for you and/or your unit or class, etc. Go to Shopping Home > Facility Supplies > MDS Warehouse (EOC Supplies). Then enter “Badger Seal” into the search box. If you’d like a box of disposable masks to go with the Badger Seals, enter “EOCGPMASK” into the search box. Note that both a free ($0).

Please note: While all campus employees are eligible to login to ShopUW+, only those employees identified by their school/college/division as Requesters can place orders for these catalog items directly.

Option #3: Here’s another “Essential Mask Brace” that’s being produced, though it’s not the Badger Seal.

Option #4 (Do-It-Yourself):  Make your own in < 5 mins. Click here for the Open Source design including detailed steps, drawings and videos.

Regardless, please fill out our interest form here and we’ll notify you once other options / updates become available.


What type is best for you? We are promoting two models: Original and Ear Loop.

[-] Original: Worn as an add-on over a mask. It has a single cord around the back of the head and can be worn comfortably for many hours:

[-] Ear Loop: Attaches to a mask at 3 locations using hook-and-loop material. The entire assembly is worn using standard ear loops. It is very easy to put on and remove, but it generally requires ear savers if worn for more than about ½ hour at a time. People with large necks, beards, etc. find that this model fits better than the original. This model can also be made out of pipe cleaner.

Quick-start Guide (watch first before using):

Detailed How-to Use Guide:

How-to Make Guide (see open source design doc here for more details):


[-] The Badger Seal was tested in a recent study: “Strategies to minimize SARS-CoV-2 transmission in classroom settings”- click here for the full research article.

[-] The Badger Seal was referenced in a recent Harvard Business Review article: “A 3-Step Strategy to Support the New U.S. Mask Mandate”- click here for the article.

Caption: Visualization using a mannequin that exhales breaths containing fog.

Below are results from tests on a classroom full of mannequins by David Rothamer and Scott Sanders at UW-Madison (reference). Aerosols were emitted by a mannequin instructor placed at the front of the room. The Effective Filtration Efficiency (EFE) was measured by another mannequin in the corner of the room near the HVAC return.

The Badger Seal (UW Fitter) is shown below to offer significant improvement in the filtration (EFE) for these types of masks tested:

[-] 3-ply disposable mask manufactured by Hodo

[-] ASTM Level II mask manufacturer by Medicom

[-] 4-ply knit cotton cloth mask

When a Badger Seal was worn over a low-cost, 3-ply, disposable mask made by Hodo, it was found to be:

[-] 4x to 8x higher effective filtration efficiency than a 4-ply knit cotton cloth mask (comparison is dependent on the type of material and the number of layers for the cloth mask).  These efficiency gains result in 15 – 18 times lower particle penetration through the mask for both inhalation and exhalation.

[-] Approximately 3x more efficient than a standard ASTM 2 surgical mask worn without a mask fitter because of the typically poor fit.

The Effective Filtration Efficiency of the disposable mask with the fitter was 95% for particles as small as 30 nm (Note: An N95 mask will have an effective filtration efficiency of at least 99% under similar conditions).

Click here for a news article summarizing a research-based guide to choosing the right mask for you, which is based on work done by members of our team and features the Badger Seal.

Caption: The Effective Filtration Efficiency (EFE) of the following four mask types were compared in a classroom setting:  a 3-ply disposable mask manufactured by Hodo, an ASTM Level II mask manufacturer by Medicom, a 3-ply mask made of spun-bond polypropylene (EOC Mask), and a 4-ply knit cotton cloth mask. Each mask was tested with (1) no fitter, (2) the Badger Seal (UW Fitter) and (3) the “Fix the Mask” (FTM) fitter shown here. More details can be found in a recent study: “Strategies to minimize SARS-CoV-2 transmission in classroom settings”- click here for the full research article.

Open Source Design:

Click here for the Open Source design including detailed steps, drawings and videos.

There’s also another version here, which doesn’t require tubing.

See our other COVID-19 projects here

This product design and specifications are being provided by the University of Wisconsin-Madison College of Engineering as a free service to the community during this public health emergency.

Regulatory Notice

This product has not been cleared for medical use by the U.S. Food and Drug Administration.  The product should only be used during the declared COVID-19 public health emergency if FDA cleared or approved products are unavailable.  This product has not been evaluated for the prevention of specific diseases or infections, the filtering of surgical smoke or plumes, the filtering of specific amounts of viruses or bacteria, or the killing or reduction of the amount of viruses, bacteria or fungi.  Not recommended for use in a surgical setting where exposure to liquid, bodily or other hazardous fluids may be expected or for use in a clinical setting where infection risk level through inhalation exposure is high.  Not recommended for use in the presence of a high intensity heat source or flammable gas.  [This product is intended for one-time use by a single user.]

Liability Notice

By using this product, the end user assumes all risks associated with its use, including the voiding of manufacturers’ warranties of devices with which the product is used, and agrees to hold harmless and waive any claims against the Board of Regents of the University of Wisconsin System, its officers, employees and agents, and other persons or companies which may have contributed to the design and specifications.  EXCEPT WHERE SPECIFICALLY PROHIBITED BY LAW, NO WARRANTIES OF ANY KIND ARE OFFERED FOR THE PRODUCT DESIGN AND SPECIFICATIONS, INCLUDING WARRANTIES OF NON-INFRINGEMENT AND FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property License

Individuals and organizations are free to use, copy, and share this design and specifications, including for commercial manufacture, without payment of any fees or charges, and for the duration of the declared COVID-19 public health emergency only, but may not assert ownership in the design and specifications, ownership of which belongs to the Board of Regents of the University of Wisconsin System and/or the individuals who created the design.

Notice to Manufacturers

Individuals or organizations that manufacture products utilizing this design and specifications are responsible for any federal or state regulatory requirements that apply to the manufacture of products intended for medical use, and are responsible for informing health care providers to which the product is supplied that they are responsible for decisions regarding appropriate personal protective equipment for their personnel.  The distribution or sale of products manufactured using this design and specifications must include the Regulatory Notice and the Liability Notice as set forth above displayed prominently on packaging and marketing materials, as well as any information required by the FDA or other governmental authorities.