Since February of 2020, we’ve been asking for standards for masks/face coverings used by our communities. Finally, the American Society for Testing and Materials (ASTM) has established a national standard for “Barrier Face Coverings” (ASTM F3502) that are neither medical masks according to ASTM F2100 standards nor respirators according to NIOSH standards. This new standard establishes minimum requirements for design, performance, and testing that will allow users to compare mask options, and provides mask makers standards to strive for. These standards are not mandatory, but can help distinguish well-tested masks in the marketplace. For home sewists and small manufacturers, the ASTM guidance can help clarify what types of testing to look for in our reading, and clarify testing goals for those headed to the lab.
Topics addressed in this post include:
- Part A: Different Masks for Different Tasks
- Part B: Overview of ASTM F3502
- Part C: What Does The Standard Mean for Mask Users, Makers, and Sewists
- Pensamientos Finales
- Appendix: A Deeper Dive into the Requirements for the Standards
Nota: Numbers in square brackets throughout the text refer to the ASTM F3502 section numbers being referenced.
Part A: Different Masks for Different Tasks
According to the CDC, masks can be used to protect yourself and to protect others. However, not all masks are created equal. The following table is adapted from the CDC’s comparison of medical masks and respirators and adds information about barrier face coverings that comply with ASTM F3502 to provide a quick comparison of the three types of masks addressed by standards in the US. Although all of these masks are designed to cover both the mouth and nose, important differences between the mask types exist in terms of intended use, face seal fit, filtration, leakage, and reuse (see table below; click on image or expand text box for details).
Part B: Overview of Barrier Face Coverings: ASTM F3502
What are Barrier Face Coverings?
Barrier Face Coverings that meet the ASTM F3502 requirements are designed to be used by the general public to cover both the mouth and nose with two primary functions:
- To provide source control by containing the user’s respiratory secretions and “reducing the number of expelled droplets and aerosols from the wearer’s nose and mouth into the air”
- To help protect the user by providing “a degree of particulate filtration to reduce the amount of inhaled particulate matter”
Three Design and Performance Criteria for ASTM F3502
To ensure that barrier face coverings provide these functions, ASTM F3502 establishes design and performance criteria in three general areas: 1) protection, 2) comfort, and 3) reusability.
|Performance Area||Evaluation Criteria|
(for yourself and others)
1. Protection: Fit and Filtration
As described in our “Big Four: Criteria for Fabric Mask Materials” post, breathability and filtration are both key factors in face mask design and materials selection. Unfortunately, the materials that most effectively block droplets and particles typically have poorer breathability, fit, and usability. Achieving a balance of these four factors is key to good mask design.
For masks designs that are not focused on creating a tight seal/fit to the face (e.g., pleated medical masks), air can leak around the edges of the mask, carrying unfiltered particles in and out. ASTM F3502 requires masks be designed to fit snugly to the face, covering both the mouth and nose, and reducing gaps. Masks must have a way of being held to the face, and sizing information should be provided. Designs must be analyzed to show that the product reduces leakage around the perimeter of the mask or other areas. Vents or valves are prohibited. [Section 5]
In general, masks that provide more filtration offer the user more protection than those that provide less filtration. However, when it comes to filtration testing, results depend strongly on the size of the particles used and specific testing methods. Studies should always be compared “apples to apples” with the same particle sizes, materials, flow rates, and humidity levels.
ASTM F3502 follows the NIOSH procedure for NaCl Aerosols Testing (TEB-APR-STP-0059), using 0.3um particles [Section 8.1]. Importantly, 0.3um is the most highly penetrant size for most materials, making this a worst case filtration test. Filtration performance against larger particles, such as respiratory droplets between 1um and 10um, is generally much higher.
The ASTM F3502 testing procedure is the same as that used to evaluate filtration performance of NIOSH respirators. While NIOSH respirators may be tested to the N95 standard (95% filtration at 0.3 um), N99 (99% filtration), etc., ASTM F3502-compliant masks can be tested to Level 1 (20% filtration), or Level 2 (50% filtration).
Importantly, unlike testing for medical masks (e.g., ASTM 2100 and EN14683), breathability and filtration testing for ASTM F3502 is conducted on completed masks rather than fabric samples. This means that results should account for materials, design, and construction techniques.
|Face Covering Type||Classification||Performance|
|Barrier Face Covering
|Level 1||≥ 20%|
|Level 2||≥ 50%|
(42 CFR 84)
Although not required by this standard, ASTM F3502 does allow mask makers to include supplemental information about bacterial filtration efficiency, which evaluates filtration of larger 3 um particles according to ASTM F2101 [9.1.7].
- Click here to see the MakerMask testing plan, which includes formal laboratory testing of three-layer fabric masks and material samples using both 0.3um NaCl aerosol testing and 3um Bacterial Filtration Efficiency Testing. We’ll share the results of this testing as soon as we hear back from the lab!
2. Comfort: Breathability
In general, masks that are more breathable are more comfortable and can be worn for longer periods of time. ASTM F3502 establishes testing requirements for mask breathability, which is measured in terms of air flow resistance. This air flow resistance is measured as the difference in pressure as air flows across the mask, where lower pressure changes correspond to more breathable masks. Once again, the testing methods are similar to those required for respirators, with different performance requirements. ASTM F3502-compliant masks have two classifications for breathability: Level 1 (lower performance: 15 mm H2O) and Level 2 (higher performance: 5 mm H2O). Both of these are more breathable than N95s, which are allowed to have air flow resistance as high as 35 mm H2O, and may require pre-use medical evaluation or be uncomfortable for some users [4.1.2; TEB-APR-STP-0007].
|Face Covering Type||Classification||Performance|
|Barrier Face Covering
|Level 1||≤ 15 mm H2O|
|Level 2||≤ 5 mm H2O|
(42 CFR 84)
|N95||≤ 35 mm H2O|
Previous breathability testing conducted on MakerMask prototypes by ATOR Labs provides examples of handmade masks constructed from between one and three layers of quilting cotton and/or nonwoven polypropylene (i.e., “basic fabric masks”) with a breathing resistance of 5.1 ± 1.2 mm H2O (n=7). Our prototype masks designed to provide increased filtration (untested, “fitted fabric masks”) had breathing resistances of 13.5 ± 2.5 mm H2O (n=4). These tests were conducted on a small number of mask prototypes (fewer than the 10 masks required by the new standard). For more information about this breathability testing, see: https://makermask.org/breathable-mask-testing-results/
Unlike medical masks and respirators, which are certified only for one-time use, the new standard for barrier face coverings provides criteria for reusability. To satisfy these criteria, barrier face coverings must include instructions for laundering, and must demonstrate that they satisfy the requirements for fit, filtration, and breathability both when new AND after the maximum number of laundering cycles specified by the manufacturer. In addition, the service life (maximum number of laundering or cleaning cycles) of the mask must be included on the mask label or package insert [11.1.4].
For those interested in more details on the ASTM standard, the see the Appendix, which takes a deeper dive into the standard and the testing requirements.
Part C: What does this standard mean for mask users, sewists, and mask?
Relevance for Mask Users
In the near future you may be able to walk into a store or hop online and buy masks that are advertised as compliant with ASTM standards, and which provide performance levels for filtration and breathability. Such labels will allow for more informed comparison shopping across a wide range of designs and materials.
In general, masks with Level 2 filtration will offer better protection than those with Level 1 protection, and masks with Level 2 breathability will be more comfortable to wear than masks with Level 1 breathability. However, in most cases masks with higher filtration performance will have lower breathability (i.e., comfort) levels.
|Level 1||Level 2|
|Filtration: Sub-micron particulate filtration efficiency (~0.3 um)
|≥ 20%||≥ 50%|
|Breathability: Air flow resistance
|≤ 15 mm H2O||≤ 6 mm H2O|
Relevance for Sewists and Makers
Face coverings that are compliant with these new standards are most likely to be produced by medium-to-large scale manufacturers that have the resources and access to accredited testing labs required to be in compliance with all the ASTM F3502 standards described above (see the Appendix for additional details on testing costs etc). However, this does not mean that sewists should stop making masks, nor does it mean that there is nothing useful in these standards for sewists and small-scale mask makers.
The Standard is Not Mandatory
First, it’s important to note that these standards are not mandatory and mask makers are not required to comply with them. At this point, we have no idea whether or not these standards will be broadly adopted by large scale manufacturers, or whether certified masks will be required for public use.
The Standard Asserts the Importance of Fit, Filtration, and Breathability
Second, although the standard doesn’t provide specific guidance on mask materials or designs, it does assert the importance of mask fit, and it establishes testing requirements and performance criteria for masks in terms of both filtration and breathability. Although testing the 10 or 20 masks required by the standard (to the tune of $2000 to $4000) may not be feasible for many, testing one or two masks (to the tune of $200 to $400) is more approachable and may provide important context for how a given mask performs relative to the standards.
MakerMask continues to follow these standards closely, and is testing prototypes using two different fabric combinations. Although this will not fully satisfy the requirements of ASTM F3502, it will provide us with representative data to compare the performance of our masks with others. We look forward to more scientific studies that leverage this standard and allow for “apples to apples” comparisons!
The Standard Can Be Used to Inform Best Practices
Finally, the ASTM standard can be used to inform ‘best practices’ for mask makers in terms of the type of information they should include with their masks:
- Donning & Doffing Instructions
- Care & Use Instructions
- Cleaning & Laundering Instructions
- Service Life (appropriate number of laundering cycles)
For those curious about how the ASTM F3502 testing requirements compare to other mask and respiratory standards, they are summarized in the figure below:MakerMask Fabric Mask Testing Results Post.
Appendix: Digging into the Details of the ASTM Standards
For those interested in the details of what is and is not required by the new ASTM standard, especially in terms of testing. This appendix dives into some of the details.
ASTM International has granted free access to COVID-19 related standards including the new ASTM F3502 standard. Click here for more information