Issued 4/7/2020

4/24/20 Revised with Surgical-style mask information

5/4/20 Revised with one-way exhalation valve information

5/26/20 Revised with private office/cubicle information

8/4/20 Revised with Penn-Provided cotton mask

8/26/20 Storage guidance removed

11/12/20 Masks may also protect you!

1/20/21 Revised Universal Mask information

2/1/21 Revised to reflect double masking 

2/10/21 KN-95 performance

3/23/21 Revised to include information about ASTM standard for face coverings 

5/25/21 Revised with new Philadelphia outdoor mask guidance

6/17/2021 Revised with indoor mask guidance

Wearing a face mask or a cloth face covering will reduce the release of respiratory droplets containing virus.  When coupled with physical distancing of 6 feet or more, mask use is highly effective in preventing the transmission of SARS-CoV-2 virus.  Because the thickness of materials used in improvised cloth face coverings and many commercially sold products can vary significantly, EHRS set minimum construction standards for masks used in Penn research buildings.  

As of Friday, June 11, 2021, in accordance with the Philadelphia Department of Public Health’s updated guidance, if you are fully vaccinated, in most situations on the University campus you do not have to wear a mask indoors or outdoors. However, we must continue to be vigilant for the members of our community who are unvaccinated and are at risk.

When are you required to continue wearing a mask?  If you are:

  1. Not fully vaccinated, the University is requiring you to wear a mask inside University buildings until further notice.
  2. A student in quarantine or isolation living with other people, also known as congregate settings. You are required to wear a mask indoors your residence.
  3. With children under the age of 12, such as a school, camp, or childcare setting.
  4. Inside healthcare settings, including all Penn Medicine facilities.
  5. Using public transportation, including Penn Transit.

Public health guidance on campus continues to evolve. Visit for current information.

Approved masks 

Surgical Masks 

EHRS recommends that Penn-affiliates wear non-medical grade surgical masks as their primary mask. Surgical-style procedure masks are constructed with three layers. The two outer layers consist of non-woven fabric made of polypropylene (typically) with densities of 20 or 25 grams per square meter (gsm). The center layer consists of a meltblown polypropylene which filters using both mechanical and electrostatic properties. This results in a mask that is highly effective at filtration with very low breathing resistance. 

Penn-Branded Cloth Face Coverings 

Penn-branded cloth face coverings, aka masks, (which were distributed by Human Resources and many schools and departments) are also approved for use in Penn research buildings.  These face coverings are made of multi-layers of cotton.  EHRS and Penn Purchasing services worked with vendors to ensure that masks purchased from approved vendors are made of thick enough cloth to adequately filter.  These masks are constructed of a minimum of 3-layers of 150 gsm cotton or 2-layers of 185 gsm cotton.     

Penn-approved cloth face coverings may be branded with the Penn-logo. Penn-approved cloth face coverings can be found here: 

Double Masking 

Surgical masks may not form a tight seal on all faces, thus reducing the effectiveness of the mask.  Concerns regarding new variants of SAR-CoV-2 that may be more transmissible has emphasized the need for improved mask protection.  Double-masking, placing a cloth face covering over a surgical mask, improves the facial seal and also provides a second filtration barrier.  Double-masking is encouraged for use at Penn; however, it may not be possible for everyone.  Double-masking is most valuable in close-distance situations in the lab, on public transit, and off-campus, where the quality of masks and proper mask wearing may be less consistent. 

Do not double-mask with two cotton face coverings, or over respirators, or masks that contain filters. This can make it difficult to breathe. The mask closest to your face must be a non-medical grade surgical-style procedure mask.  The second mask, worn over a surgical-style mask, may be a Penn-branded cotton cloth face covering or any home-made or purchased face covering. See Maximizing Fit for Cloth and Medical Procedure Masks to Improve Performance and Reduce SARS-CoV-2 Transmission and Exposure.

Face Shields 

CDC does not recommend using face shields as a substitute for masks. However, when combined with a mask, a face shield protects the eyes of the person wearing it. Face shields must be used when lab work makes it impossible to maintain distancing. Choose a face shield that wraps around the sides of your face and extends below your chin or a hooded face shield. This is based on the limited available data that suggest these types of face shields are better at preventing spray of respiratory droplets. See


You should reuse your surgical-style mask until it becomes torn, visibly soiled or hard to breathe through.  Cloth masks provided by your supervisor should be laundered daily at home using household supplies.

One-way Exhalation Valves

One-way exhalation valves, which permit unfiltered air to be released by a mask or respirator, are not permitted.


Exhalation valve examples

Use of KN-95 Respirators 

The use of any respirator by Penn affiliates for compliance with Universal Masking requirements is not permitted.  All respirators including N95s and KN-95 are personnel protective devices that are regulated by OSHA.  Use of respirators in the workplace, even when purchased by the employee, without annual medical clearance, fit testing and training is a potential violation of OSHA regulations.

Wearing a respirator that does not fit your face will not provide additional protection.  In December EHRS quantitatively fit tested 18 faculty/staff members to compare 3 different KN95 style face masks and a standard surgical mask.  Testing was performed because staff felt that the KN95 style face mask would provide better respiratory protection than surgical masks during close proximity work.    

The results indicated that the KN95s did not provide better protection.  In all but three cases, the surgical mask, with modifications to bring the sides closer to the face (such as twisting the ear loop, tying a knot close to the mask, and folding the material) had an improved fit compared to the KN95. 

Last summer EHRS fit tested approximately 1100 Penn Dental students and medical practitioners with a limited variety of N95 and KN-95 respirators.  We abandoned the KN-95s early on because limited fit-test success.

EHRS believes that double masking with a non-medical grade surgical mask and a cloth face covering will ensure better protection than wearing an unfitted KN-95 or N95 respirator.  See Maximizing Mask Fit.

ASTM Standard for the Testing and Rating of Barrier Face Coverings 

ASTM International recently published a standard (ASTM F3502) for the testing and rating of barrier face coverings. The intent of the standard is to establish uniform testing criteria for respiratory droplet source control, filtration, breathability, and labeling of face coverings.  This standard allows end users to directly compare the performance of different mask products.

Barrier face coverings are primarily intended for source control, and the new standard specifies that face coverings must fit snugly to the face to reduce the spread of respiratory droplets. Additionally, the new standard requires that the face covering filter out at least 20% of small airborne particles to provide some degree of protection to the wearer, and that face coverings must have low air resistance so that the face covering is breathable and comfortable. The standard contains testing criteria for reusable face coverings as well as single-use face coverings. The label “MEETS ASTM F3502” will be printed on face coverings that have been determined to meet these specifications by an accredited testing laboratory.  As companies obtain ASTM F3502 certification, EHRS will provide campus guidance on these masks.