Mask Material Testing Plan

Update (February 12, 2021): Thanks to our generous community and a grant from Helpful Engineering, we exceeded our fundraising goal for mask testing!  In addition to the originally planned fluid resistance, breathability, and bacterial filtration testing of our fabric combinations, we were able to add mask-level NaCl aerosol filtration tests to our campaign. Thank you to everyone that donated to this testing campaign.

As regular readers of MakerMask know, we have been hard at work fundraising for our next round of laboratory mask testing.

• MakerMask Lab Testing Campaign

This post shares more details on what we plan to test and why.

Why do we need this testing? 

There is a disconnect between the materials available to sewists making fabric masks for COVID, and the materials being tested by the scientific community.  Some of the published literature uses informal tests or equipment that cannot be reproduced.  Others do not tell us enough about the specific masks and materials being tested to be useful.  This makes it hard for sewists to interpret and decide on optimal mask materials and layering combinations for homemade masks.

What is our goal?

Our goal is to provide open access, quantitative, head-to-head (i.e., apples-to-apples) data that is consistent with regulatory testing standards to help fabric mask makers select more effective materials and layering combinations for COVID-19. 

Who benefits from this testing? 

Mask users and mask makers (sewists, maker spaces, and small manufacturers) looking to make data-driven mask material decisions.

Which materials/combinations are we going to test? 

With our initial fundraising targets, MakerMask plans to test two different 3-layer fabric combinations and to establish baseline performance relative to surgical mask standards.  In this round of testing, we are primarily focused on two materials: 

1. Spunbond nonwoven polypropylene (NWPP)
2. Tightly-woven quilting cotton

For more information about how/why these materials were selected, please see “Finding and Selecting Polypropylene for Fabric Masks.” 

Selected mask materials

To help the mask making community, we have selected easily sourced products that we believe work well for community production. (Note: these are not endorsements or explicit vendor-approved uses of the materials.)

As shown in the tables below, we will initially be testing 3-layer masks made with Smart-fab® DoubleThick NWPP, as well as 3-layer masks with a combination of Smart-fab® and Kona® quilting cotton.  (If we are able to raise additional funds, we look forward to adding additional materials and combinations to the test campaign!) 

Table 1. Selected mask materials for layering.

Fabrics	Description	Fabric Weight (gsm)	Preferred Location Within Mask	Safety Information from Manufacturer/Distributor
Spunbond NWPP	Smart-fab® DoubleThick (Available Online)	67 gsm	Outer Middle Inner	Smart-fab is washable, “was tested and approved to be compatible with the Fire Flammability Act Standard (16 CFR, part 1610)” http://www.smartfab.com/FAQ
Quilting Cotton	Kona® Quilting Cotton (Robert Kaufman Fabrics, Natural)	148 gsm (4.35 oz/yd2)	Outer Inner	Kona has been “tested for harmful substances according to oeko-tex 100 standards” and “is harmless for human health” – https://www.oeko-tex.com/en/our-standards/standard-100-by-oeko-tex

Table 2. Layering of mask materials. Preliminary testing will focus on the first two combinations, highlighted in yellow. If possible, future campaigns may include all four options.

Designs	3–Layer Mask Material Combinations
	Skin Contacting	Middle	Outer
#1. MakerMask Original	NWPP	NWPP	NWPP
#2. Sewists Choice – Common sewist combination & Health Canada Recommendation	Cotton	NWPP	Cotton
#3. World Health Organization compliant	Cotton	NWPP	NWPP
#4. Disposable Filter Insert – WHO compliant, not washable, enhanced filtration	Cotton	Filti®	NWPP

Which tests are we performing? 

Testing standards for handmade fabric masks are evolving (ASTM standard in progress). Although fabric masks are not medical masks, we aspire to meet the same laboratory test criteria (i.e., “Surgical Masks EUA Template for Addition to Appendix A”, EN14683, and ASTM F2100). 

Primary Testing Goals

Our primary goals with this round of testing are to evaluate these material combinations for: 

1. Fluid resistance — Do the samples block splashes and sprays (liquid droplets that are 10 microns or larger, >10 um)?
2. Bacterial filtration efficiency — Do the samples filter mid-sized droplets and particles (1 – 3 um)?
3. Breathability — Do the samples allow air to freely pass through them?

Table 3 provides more detailed information on these tests, and highlights the testing required by European Standards (EN14683) as well as some of the typical testing required by the FDA for medical masks sold in the U.S..  For additional descriptions, see MakerMask’s previous blog posts on fluid resistance y breathability testing.

Table 3. Initial medical/surgical mask testing requirements for European Standards (EN 14683) and U.S. (FDA 510 k). Quotes are from CTT Labs y Nelson Labs.

Test of Fabric Samples	Testing Standard	Number of Samples Required	Laboratory Test Pricing per Material Combination
#1. Fluid Resistance	EN14683 or ASTM F1862	30-40	$400 – $600 USD
#2. Bacterial Filtration Efficiency (~3um)	EN14683 or ASTM F2101	5	$1160 – $1400 USD
#3. Breathability	EN14683 o ASTM F2100	5	$300 – $600 USD

Why Have We Prioritized Bacterial Filtration Efficiency? 

Nelson labs summarizes it well: 

• The BFE test offers a number of advantages over other filtration efficiency tests. It has been used with little or no modification for years and provides a standard reference for comparison of filtration materials. 
• The mean particle size can be tightly controlled and is sized using a six-stage viable-particle Andersen sampler, permitting stage-by-stage analysis. 
• The BFE procedure is reproducible, and provides a more severe challenge to most filtration devices than would be expected in normal use. 
• Large numbers of material can be evaluated in a relatively short time.

For more information see: https://www.nelsonlabs.com/testing/bacterial-viral-filtration-efficiency-bfe-vfe/ 

Stretch Goal

Due to the success of our fundraising campaign, we’ve been able to add a stretch goal of evaluating the NaCl aerosol filtration of sample masks to our testing plan. These masks are constructed from the same two material combinations discussed above:

• NaCl Aerosol Filtration — Do the mask prototypes filter small (sub-micron) particles (0.3 um)?

Table 4 provides additional information on NaCl Aerosol testing, which is traditionally used to evaluate the performance of N95 respirators. It is important to note that fabric masks are not expected to perform nearly as well as N95s in this test. However, performance characteristics may aid users in selecting between fabric mask options.

Table 4. Fabric mask testing methods for evaluating performance at 0.3um.  Highlighted rows are targeted for current MakerMask testing. Quotes are from CTT Labs y Nelson Labs.

Test of Fabric Mask	Testing Standard	Number of Masks Required	Laboratory Test Pricing per Material Combination
NaCl Aerosol (~0.3um)	42 CFR Part 84 or NIOSH N95	3 – 20	$645+ USD

Thank You!

A special THANK YOU to all our supporters who have contributed to make this valuable testing possible!  To make a tax-deductible donation in support of MakerMask’s research and education efforts, please visit: https://charity.gofundme.com/o/en/campaign/makermask-testing