The Big Four: Criteria for Fabric Mask Materials for COVID

This deep dive post looks into the “Big Four” criteria evaluated in preliminary assessments of fabric mask materials: 1) material characteristics, 2) breathability, 3) water-resistance, and 4) disinfection options. More specifically, we focus on spunbond nonwoven polypropylene (NWPP), which is commonly used in commercial face masks. Here we take a more in-depth look at the 4 preliminary criteria considered when evaluating potential sources of spunbond NWPP.

1. Mask Material Characteristics & Sourcing

MakerMask designs use community-sourced 100% spunbond nonwoven polypropylene. Although ideal medical grade NWPP is not currently available for community use, spunbond NWPP is available at different weights and grades for other household and/or commercial purposes, such as reusable grocery bags, some craft fabrics (e.g., Smart-Fab and Oly-Fun), and some sew-in interfacing.

Standard measurements of fabric weight (gsm or oz/yd²)

Fabrics may be characterized in a number of different ways, a standard measurement for fabric weight is grams per square meter (gsm) or ounces per square yard (oz/yd²). Although either set of units can be used (e.g., 50 gsm = 1.47 oz/yd², 100 gsm = 2.95 oz/yd²), we will use gsm throughout our discussions. For those more familiar with ounces and yards, check this Herramienta práctica de conversión.

Click here for more on mask fabrics and fibers

Although medical grade NWPP (20 – 25 gsm) is used in commercial masks and respirators, for ethical reasons these materials are currently reserved for manufacturers that best meet medical, legal, and regulatory standards. Given that these medical grade NWPP materials are not widely available to the public at this time, the preferred sources of spunbond NWPP for use in community masks has been bolsas reusables de compras.  (~70 – 100 gsm). However, NWPP from reusable grocery bags is not readily available to sewists and mask makers by the yard. As a result, spunbond NWPP that is more commonly available by the yard (i.e., that used in clothing, textiles, crafting, and upholstery applications) is being investigated for suitability for use in masks. Recent testing results of the breathability, filtration, and fluid resistance of spunbond NWPP used in some craft applications (i.e., SmartFab Backgrounds, ~65 – 70 gsm) suggests it may be a good choice for use in community masks.

Mask Material Identification: Spunbond NWPP

Some sources of spunbond NWPP (e.g., bags constructed from 100% Spunbond NWPP) may be identified by either a tag indicating “100% Polypropylene,” or the indicador de reciclaje “#5 PP”. In addition to material composition, it is important to identify the spunbond nonwoven structure of the material. This can be accomplished by looking for the characteristic diamond-shaped dimpled pattern.

TOP CHOICES: Reusable Grocery Bags (typically 70 – 100 gsm)

Spunbond bolsas PPNT de comprar comida are designed to be in contact with food and have a greater consistency in material properties, manufacturing, and safety than materials used for things like craft projects and landscaping. Since they are designed to carry food, they have minimal particle shedding, and are designed to withstand washing and/or disinfection. Spunbond NWPP materials provide a balance of water-resistance, mechanical filtration, and breathability. Although NWPP bags are thicker than many materials, they work well as mask layers (especially outer layers).

NOTA: Do not use bags that are finished with a laminated waterproof coating or bonded to insulation as these may compromise breathability.
NOTA: Spunbond NWPP Conference Bags (typically 60 – 90 gsm) may also be considered: The material weight of conference/promotional bags is more variable than that of reusable grocery bags, and often includes lighter weight and/or softer materials.

Deeper Dive: Characteristics of polypropylene in reusable bags

“Isotactic polypropylene [all the methyl groups are lined up on the same side of the polymer chain] is generally used for commercial purposes due to its high melting point; its ability to withstand heat makes for a mejor alternativa al plástico. Éste polímero resistente al calor es benficial para bolsa reusables para comprar comida, que se espera llevar artículos de variadas temperaturas. Polipropileno cae bajo la categoria de termoplásticos, significando que puede ser ablandado y formado cuando se calienta mientras retiene su estructura y durabilidad. Polipropileno repela agua naturalmente, por lo tanto hace más fácil limpiar las bolsas reusables para comprar comida. Un material que se puede desinfectar fácilmente es especialmente importante ya que la bolsas reusables frecuentemente están expuesto a la bacteria mientras contienen comida cruda. Una revisión hecho sobre el proceso de spun bonded reconoce polipropileno isotáctico como el material más económicamente eficaz, porque es más económico y produce lo más fibras por kilogramo (Lim 2). Ya que la orden de las fibra no importa, más tela resulta porque toda la material termina siendo apretado junta (Kansal 9).”

TOP CHOICES: SmartFab Backgrounds (typically 65 – 70 gsm)

Smartfab Backgrounds (aka doubleweight) is 65 to 70 gsm crafting material constructed from 100% NWPP. Recent laboratory testing of multi-layer Smart-Fab samples and mask prototypes suggest that it may be a good choice for use in community masks based on its performance relative the ASTM F3502 barrier face covering standards.

Click here for more information on mask testing results (consistent with ASTM F3502 & ASTM F2100) for spunbond NWPP craft fabrics

CUIDADO:

Safety and usability of NWPP from alternatively sourced materials cannot be assumed. Special caution is recommended advised when considering meltblown NWPP, fusing interfacing, landscaping materials, surgical barrier materials, and crafting materials.

Materials Selection FAQ

¿Es igual todo el polipropileno no tejido?

NO. As with all textiles, there are different thicknesses and grades of NWPP. This is one of the reasons that we can’t guarantee or vouch for the effectiveness of hand-made masks from alternatively sourced materials.

Click here for more information about the different types of polypropylene

¿Como evaluar si mi PPNT funcionará para una máscara?

When you flick water at the fabric, you want to see the water droplets bead up and roll off, while the inside stays dry. You also want to make sure that the material is breathable. If it passes both of those tests, that is the evidence you are looking for that it will make a better-than-better-than-nothing mask.

Click here for DIY tests you can do at home to evaluate you mask materials

What about meltblown NWPP?

Meltblown NWPP may pose inhalation risks. Meltblown NWPP tears easily, is harder to sterilize, lacks the diamond pattern, and is not used in reusable NWPP grocery bags. Although melt-blown is made from the misma materia prima que PPNT spunbond, la estructura del material, y el tamaño de las fibras son diferentes. Las fibras de PPNT soplado por fusión are both shorter and thinner, which increases the risk of particle inhalation. For large-scale commercial mask operations with appropriate manufacturing controls and oversight, these risks can be mitigated; however, for home sewists the use of meltblown NWPP is not generally recommended at this time due to potential for occupational exposure while cutting, sewing, handling, and constructing unfinished meltblown materials.

Click here for a deeper dive into meltblown NWPP and other mask fabrics

What about interfacing?

NWPP interfacing that contains adhesives should not be used in DIY masks. Although interfacing without adhesive (e.g., sew-in interfacing) may ok for use, NWPP in interfacing is frequently made using different manufacturing processes and standards than the spunbond NWPP in reusable grocery bags. Its suitability for use as droplet protection in masks is under investigation.

What about landscaping cloth and geotextiles?

NWPP from landscape cloth and other geotextiles may pose inhalation risk. The fibers in these materials are prone to shedding and may pose risk of mechanical irritation when inhaled. In addition, preliminary data from particle testing sugiere pobre rendimiento de filtración, y no siempre son resistentes al agua. 

What about surgical barrier materials?

[Added: May 17, 2020] In nonwovens used as barriers in other medical applications like gowns and surgical drapes, water-resistance and water-repellence may be achieved by chemically treating or coating the materials. These treatments allow materials to gain regulatory approval at higher barrier standards but may not be suitable for use in masks. Check manufacturers’ information on materials used for possible hazards (Jones, 2005).

¿Qué pasa con bolsas de aspiradora? Leí que son excelentes para filtrar. 

Como muestra éste papel showed, vacuum cleaner bags are very good at filtering, but they have a higher pressure drop, meaning they aren’t particularly breathable. We recommend sticking to more breathable options, especially for well fitted mask designs.

What about 'Oly-fun'?

Many sites list ‘oly-fun’ as 65 gsm 100% NWPP. It’s suitability for use in masks is under investigation and discussed in greater detail in the finding and selecting polypropylene for masks post linked below. Preliminary results suggest it’s performance may be similar to that of SmartFab Backgrounds.

For more information see: Finding and Selecting Polypropylene for Washable Masks

What about olefin?

Olefin es tipicamente una mezcla de polipropileno y polietileno, que baja significamente el punto de fusión del material. Éste material derriterá/achicar al ser hervido y no se debe usar en los diseños de MakerMask.

What about nonwoven polyethylene?

El punto de fusión de promedia polietileno comercial de baja densidad es tipicamente 105 a 115o C (221 a 239o F), que lo hace inadecuado para los procedimientos de desinfessión propuestos. 

2. Respirabilidad

Breathability is an important factor in face mask design and materials selection. Unfortunately, the materiales que bloquean gotitas y partículas más efectivamente, típicamente tienen respiribilabilidad, ajuste, y usabilidad mal. Preliminary breathability checks for novel masks/materials frequently begin with qualitative functional assessments from developers and users. However, quantitative analysis of breathability, including tests of the pressure drop across the mask and CO₂ accumulation, are important for verifying usability. For masks designs that are not focused on creating a tight seal/fit to the face (e.g. pleated masks), both air and CO₂ pueden escapar alrededor de la máscara. Para máscaras ‘evaluado para ajuste’ con buen ajuste y requisitos para filtración de partículas submicron, éstas medidas de respirabilidad llegan a ser críticas para el éxito de la máscara.

Fabric Layering Combinations

Investigación sobre el número óptimo de capas de PPNT sigue, sin embargo datos preliminares del laboratorio suggests that three layers of spunbond NWPP provides adequate breathability for diseños de máscaras ajustadas y no ajustadas. Despite qualitative assessment to the contrary, masks with additional layers began to show decays in performance (e.g., increased pressure differential across the mask and suboptimal CO₂ accumulation). The ideal number of layers of NWPP will vary depending on the individual materials used and the trade-off between usability, breathability, particle filtration, and intended duration of use. Optimization and evaluation of prototypes, materials, and designs is ongoing.

Update: New guidance from the WHO recommends 3 layers (June 5, 2020)

New guidance from the WHO (June 5, 2020) recommends masks consisting of 3 layers including a combination of both hydrophilic and hydrophobic layers. For details see post about updated guidelines.

Is Halyard H600 Surgical Wrap breathable?

Pregunta activa: ¿Cumplen con estandares de respirabilidad máscaras hechas de envoluntura quirúrgica Halyard H600? Máscaras hechas de H600 are gaining traction in medical communities and the benefits of H600 are indisputable: it has great particle filtration data, it is sterilizable, and is commonly available in hospital settings. However, uncertainty surrounding quantitative assessments of the breathability and the delcaraciones de Halyard que niegan el uso fuera de etiqueta sugieren que se merece un enfoque cauteloso may be merited.

Edit: November 23, 2020. Two recently released publications (November, 2020) evaluated the breathability of H600 sterilization wrap, and both concluded that H600 is not recommended for use in masks because the breathing resistance is too high:

Grigg SE, Zampiron A, Akbaridoust F, et al. Are surgical masks manufactured from sterilisation wrap safe? [published online ahead of print, 2020 Nov 19]. Infect Dis Health. 2020;doi:10.1016/j.idh.2020.11.001. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7674969/
Sousan S, Garcia N, White A, Balanay JA. Filtration Efficiency of Surgical Sterilization Fabric for Respiratory Protection during COVID-19 Pandemic [published online ahead of print, 2020 Nov 6]. Am J Infect Control. 2020;S0196-6553(20)30974-3. doi:10.1016/j.ajic.2020.11.005 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7647410/

¿Sabías que? Electrostatic treatments and breathability

Sin tratamiento electrostático, la mayoría de los materiales que tiene 1um o mejor de filtración se comprometen respirabilidad. Por eso las materiales con la mejor filtración de partículas frecuentemente son mal adaptados para uso en máscaras caseras. Los materiales especialmente fundidos para filtros que están usados en máscaras N95 para obtener filtración excelente requieren tratamientos especiales (p.ej. Tratamiento Coraona o Tratamiento Electret) para lograr óptima actuación de filtración de partículas. Más información sobre la producción de máscaras médicas.

PRECAUCIÓN: NO USE.

The following materials do not have sufficient breathability for use in DIY masks: Laminated waterproof bags, Evolon, Vacuum Cleaner Bags, HEPA Filters, et al.

3. Droplet Resistance

Según el CDC, gotitas >5 μm en tamaño han sido implicadas en la transmisión del virus del gripe, adenovirus, rinovirus, y el coronavirus, asociado al SARS (SARS-CoV). Para información adicional sobre precauciones contra gotitas, ve las pautas oficiales del CDC. In the context of face masks: “Fluid resistance is defined as the ability of a facemask’s material construction to minimize fluids from traveling through the material and potentially coming into contact with the user of the facemask.”

Fluid Resistance

Fluid resistance helps reduce potential exposure to blood and body fluids caused from splashes, spray or spatter [Infection Control Today, 2003].” For FDA-regulated medical masks, fluid resistance is measured as the “Resistance to Penetration by Synthetic Blood…as specified in Test Method F 1862.” Although this test is performed using synthetic blood, it is the generally used to establish the fluid resistance of masks such as those used for droplet protection [ASTM F1862 / F1862M – 17; Midha et al, 2012].

[Update: October 14, 2020] MakerMask had 40 samples of 3-layer spunbond NWPP tested according to ASTM F1862 fluid resistance testing standards. Our samples passed at a level higher than we anticipated (ASTM Level 2). Click here for details and the full report Fluid Resistance.

Water Resistance

Information is available on the water resistance of spunbond NWPP materials such as those used in MakerMask designs. Spunbond NWPP is naturally hydrophobic (water-repellent).

DIY Home Test for Water Resistance

A quick qualitative assessment, a ‘flick’ test, can be performed to see if water beads up on the surface of the material (suggesting it is hydrophobic), or if it saturates into the fabric (suggesting it is hydrophilic).
Quantitative assessment of the passage of water through mask materials over a given interval of time (e.g. 60 seconds or 1 hour) can be realizadas por desarolladores de máscaras y users at home.

Pot of Boiling water for disinfection of fabric masks made with nonwoven polypropylene

4. Desinfección

[Update April 11, 2020] Click here for our post with research and details on mask cleaning and disinfection methods

The fourth key factor for MakerMask designs is whether or not the full mask can be disinfected before use. The current recommendation for home use is to boil masks for 10 minutes prior to use. This procedure was established because “boiling is sufficient to kill pathogenic bacteria, viruses and protozoa (WHO, 2015)”. La duración maximiza desinfección de todas las capas de la máscara. Hervir como un método estandarizado de desinfección casera provee una consistente temperatura máxima bastante debajo del punto de fusion/deformación del PPNT spunbond 100% usado típicamente para bolsas reusables de comprar comida.

Deeper Dive into the melting point of spunbond NWPP

The melting point of polypropylene occurs in a range. 100% NWPP used in high-quality re-usable grocery bags/conference bags is primarily isotactic polypropylene, which has a melting point between 160 to 166 °C (320 to 331 °F) and is safe to boil (100 °C / 212 °F), steam (121 °C / 250 °F), and/or autoclave. Industry guidance for decorating spunbond NWPP tote bags (for groceries/conferences/promotional purposes) suggests that, “bolsas no deben ser planchados a más de 275 grados sin experimentando fusión menor de la tela. Algunas transferencias que calientan a los 300 grados pueden ser usados, sin embargo algunas bolsas pueden experimentar fusión menor a ésta temperatura.” NOTA: El uso de ollas a presión para esterilización a vapor (hasta 121C / 250F) ha sido sugerido, pero éste método de esterilización permanece sin evalución, no verificado por ahora. 

A pesar de que procedimientos adicionales para desinfección han sido propuestos, no todos han sido evaluados para éste propósito. En general, químicos agresivos (p.ej. blanqeudora) no están recomendados as residual chemicals in the mask may cause unintended inhalation risks. In addition, oxidizing chemicals may cause the mask materials to degrade more quickly. The longevity of use of community spunbond NWPP masks is currently under investigation.

While awaiting more quantitative evaluation, two qualitative indicators indicate reduction of the functional characteristics of the mask:

Water-resistance, when water stops beading on the surface during the ‘flick’ test, the droplet protection is degrading and the mask should be retired,
Shedding, when the bonding of the fibers to the mask starts to degrade and the material starts shedding, the mask should be retired from use as dislodged threads could act as lung irritants (NOTE: landscape cloth and other geotextiles typically fail this assessment prior to first use).

Washing and Disinfection FAQ

¿Cómo se lava polipropileno no tejido?

Although hand washing and hang drying is preferred, spunbond NWPP fabric can be machine washed (warm) and hung to dry. Rinse thoroughly, and do not use fabric softener. Avoid using bleach or alcohol on these fabrics, because those chemicals break down the properties that make NWPP a good choice. Before use, MakerMask masks can be disinfected with boiling water or in hospital autoclaves.

NOTE: If washing masks with soap or detergent, be sure to rinse thoroughly as soap residues may compromise water resistance.

[Update May, 2021] Click here for our post with general information about washing masks containing spunbond NWPP.

¿Debo planchar la máscara? ¿Y cuando estoy haciendo los pliegues? 

PPNT se sabe que se derrite con algunas planchas y podria dañar ambos la máscara y su plancha. Por éste razón, no recomendamos planchar. Si lo hace, use precauciones para tela sensitiva/delicada como el ajuste de calor más bajo y colocando una toalla entra la máscara y su plancha.

Should I disinfect my mask with a UV box?

It is important to note that ultraviolet irradiation methods are “unlikely to kill all the viruses and bacteria” in face masks with multiple layers, pleats, and/or seams. UV is not recommended for disinfection of multi-layer masks.

Should I heat my mask in a dry oven at 70C to disinfect my mask?

Dry heat is not recommended for MakerMask designs. Although some studies have shown that particle filtration efficiency remain OK with that dry heat at temperatures of 70°C for 30 minutes, the effectiveness of that temperature and duration of dry heat is less clear. It may be hot enough, for long enough to kill COVID-19, but the research suggests it may not be effective for killing other pathogens (e.g. bacteria) that may be growing on the mask. It is important to note that for dry heat sterilization the required temperatures are more than double 70°C, and the required times are also doubled.

Furthermore, dry heat sterilization is less effective than moist heat sterilization, and dry heat sterilization is not generally recommended for polypropylene. According to the CDC, “Dry-Heat Sterilizers: This method should be used only for materials that might be damaged by moist heat or that are impenetrable to moist heat (e.g., powders, petroleum products, sharp instruments). The advantages for dry heat include the following: it is nontoxic and does not harm the environment; a dry heat cabinet is easy to install and has relatively low operating costs; it penetrates materials; and it is noncorrosive for metal and sharp instruments. The disadvantages for dry heat are the slow rate of heat penetration and microbial killing makes this a time-consuming method. In addition, the high temperatures are not suitable for most materials. The most common time-temperature relationships for sterilization with hot air sterilizers are 170°C (340°F) for 60 minutes, 160°C (320°F) for 120 minutes, and 150°C (300°F) for 150 minutes. B. atrophaeus spores should be used to monitor the sterilization process for dry heat because they are more resistant to dry heat than are G. stearothermophilus spores. The primary lethal process is considered to be oxidation of cell constituents.”

PRECAUCIÓN:

Los materiales PPNT usados para artesanía, coser, y otros propósitos pueden derrietirse aunque están listados como 100% polipropileno porque éstas materiales están frecuentemente compuestos de formas menos critalinos de PP con puntos de fusión más cerca a 130o C (266o F). Aunque estos materiales pueden ser lavables, pueden deformar y/o derretirse al ser hervidos, planchados, cuando se cuece al vapor o esterilizado en autoclave.

Final Thoughts on Spunbond NWPP

Algunos benefits of spunbond NWPP include that it is: commonly available in non-woven grocery bags and conference bags, hypoallergenic, water-resistant, conducive to mechanical filtration, and can be disinfected by boiling. Potential drawbacks of community-sourced spunbond NWPP include difficulties identifying suitable materials and variability in NWPP density and structure. These drawbacks can be mitigated by sourcing from more homogeneous subsets of spunbond NWPP based on use case. For example, reusable grocery bags are designed for the same use (carrying loads of food), have more consistent standards for strength, durability, quality, disinfection, and higher melting points than NWPP from other sources.

[Edit: June 26, 2020] For additional information about testing mask materials check out: 3 Easy DIY Mask Tests

Photo: DIY Mask Testing Setup for Fabric Materials. Photo includes spunbond nonwoven polypropylene mask, teaspoons, scale, elastic band glass, and cotton ball

For information about “window masks” or “clear face covering” check out: “5 Key Considerations for Window Masks.”

Select References/Links

Additional References/Links

CDC: Strategies for Optimizing the Supply of N95 Respirators: Crisis/Alternate Strategies, Health Care Provider use of non-NIOSH approved masks or homemade masks. Accessed at https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirators-strategy/crisis-alternate- strategies.html on March 15, 2020
Dato, V. M., Hostler, D., & Hahn, M. E. (2006). Simple respiratory mask. Emerging infectious diseases, 12(6), 1033–1034. https://doi.org/10.3201/eid1206.051468. Accessed at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3373043/ and https://wwwnc.cdc.gov/eid/article/12/6/05-1468_article on March 12, 2020 (Figure Below)
Rengasamy S, Eimer B, Shaffer RE. (2010) Simple respiratory protection–evaluation of the filtration performance of cloth masks and common fabric materials against 20-1000 nm size particles. Ann Occup Hyg. 2010;54(7):789–798. doi:10.1093/annhyg/meq044. Accessed at https://pubmed.ncbi.nlm.nih.gov/20584862-simple-respiratory-protection-evaluation-of-the-filtration-performance-of-cloth-masks-and- common-fabric-materials-against-20-1000-nm-size-particles/ o https://academic.oup.com/annweh/article/54/7/789/202744 on March 12, 2020. “Fabric materials may provide some level of protection against the transmission of infectious aerosols when used in combination with other protective measures.”
Institute of Medicine. 2006. Reusability of Facemasks During an Influenza Pandemic: Facing the Flu. Washington, DC: The National Academies Press. https://doi.org/10.17226/11637. Accessed at https://www.nap.edu/read/11637/chapter/6#62 on March 12, 2020
Van der Sande, M., Teunis, P., & Sabel, R. (2008). Professional and home-made face masks reduce exposure to respiratory infections among the general population. PloS one, 3(7), e2618. https://doi.org/10.1371/journal.pone.0002618, Accessed at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440799/
Mueller et al (2018). The effectiveness of respiratory protection worn by communities to protect from volcanic ash inhalation. Part I: Filtration efficiency tests. International Journal of Hygiene and Environmental Health Volume 221, Issue 6, July 2018, Pages 967-976. Accessed at: https://www.sciencedirect.com/science/article/pii/S1438463917308003
Davies A, Thompson KA, Giri K, Kafatos G, Walker J, Bennett A. Testing the efficacy of homemade masks: would they protect in an influenza pandemic?. Disaster Med Public Health Prep. 2013;7(4):413–418. doi:10.1017/dmp.2013.43 Accessed at https://pubmed.ncbi.nlm.nih.gov/24229526-testing-the-efficacy-of-homemade-masks-would-they-protect-in-an-influenza-pandemic/
Adam Burgess Mitsutoshi Horii (2012). Risk, ritual and health responsibilisation: Japan’s ‘safety blanket’ of surgical face mask‐wearing. Sociology of Health and Illness 34(8) 1184-1198. https://doi.org/10.1111/j.1467-9566.2012.01466.x, Accessed at: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1467-9566.2012.01466.x
Advice on the use of masks1 in the community setting in Influenza A (H1N1) outbreaks. https://www.who.int/influenza/preparedness/measures/Adviceusemaskscommunityrevised.pdf
Non-occupational Uses of Respiratory Protection – What Public Health Organizations and Users Need to Know. https://blogs.cdc.gov/niosh- science-blog/2018/01/04/respirators-public-use/
How do respirators actually work? https://www.uvex-safety.com/blog/how-do-respirators-actually-work/
Can DIY homemade masks protect us from coronavirus? https://smartairfilters.com/en/blog/diy-homemade-mask-protect-virus-coronavirus/
What are the Best Materials for Making a DIY Face Mask? https://smartairfilters.com/en/blog/best-materials-make-diy-face-mask-virus/
DIY masks: Is paper towel effective at blocking viruses? https://smartairfilters.com/en/blog/paper-towel-effective-against-viruses-diy-mask/
Spunbond nonwoven Polypropylene Materials
1. https://www.superiorfelt.com/products/air-filtration-media/sub-micron/personal-protection/
2. https://blogs.cdc.gov/niosh-science-blog/2009/10/14/n95/
3. Medical Face Mask Machine: The Complete Guide for the Medical Masks Production. https://www.testextextile.com/fighting-the-coronavirus-top-6-knowledge-to-know-before-investing-in-establishing-disposable-medical-mask-production-lines/ , “The core material of medical masks is polypropylene melt blown non-woven fabric after electret treatment. The filtering mechanism of medical masks is Brownian diffusion, entrapment, inertial collision, gravity sedimentation and electrostatic adsorption. The first four are physical factors, that is, the characteristics of the non-woven fabric produced by the melt blown method, the filterability is about 35%; this is not up to the requirements of medical masks, we need to electrotype the material and let the fiber Charged and used static electricity to capture the aerosol where the new coronavirus is located.”
4. https://www.slideshare.net/muralikrishnan71697092/respiratory-protection-face-masks-and-respirators
Non-woven Polypropylene In Masks: Links
1. Example (https://www.nonwovenproductsupplier.com/products/3Ply-Nonwoven-Face-Mask.html): 1st ply: 20g/m2 spun-bond PP, 2nd ply: 25g/m2 melt-blown PP (filter), 3rd ply: 25g/m2 spun-bond
2. Nonwoven polypropylene fabric usages (https://www.pp-nonwoven.com/medical-fabric-use-face-mask_p358.html):
3. https://www.smartbags.co.uk/blog/bag-for-life-fabric-explained-non-woven-polypropylene-nwpp
4. Non-woven: https://www.greatlakesfilters.com/non-woven-textiles/

17. NWPP Sterilization/Disinfection Information

Ozone & Polypropylene: https://www.cdc.gov/infectioncontrol/guidelines/disinfection/sterilization/other-methods.html
https://www.cdc.gov/infectioncontrol/pdf/guidelines/disinfection-guidelines-H.pdf
https://www.hmcpolymers.com/uploads/files/resources/hmc-pp-chemical-resistance.PDF, “Polypropylene offers good resistance tonon-oxidizing acids and bases, fats and most organic solvents; The melting point of polypropylene is 160°C / 320°F; Low temperature threshold: polypropylene becomes brittle below 0°C; NOT compatible with strong oxidants. According to ASTM D570, its 24 hr water absorption rate is 0.03%. It resists most strong mineral acids and bases, but, like the other polyole-ns, it is subject to attack by oxidizing agents. PP resins are appreciably affected by chlorosulfonic acid and oleum at room temperature, 98% sulfuric acid, 30% hydrochloric acid, and 30% hydrogen peroxide at 100°C (212°F).”

https://www.industrialspec.com/resources/plastics-sterilization-compatibility/, “Steam Sterilization, also known as autoclaving, involves generating or injecting saturated steam into a pressure chamber at a temperature range of 121-148 °C (250-300 °F) at 15psi for a period of time sufficient to provide sterilization.
Additional References: Alariqi SAS, Mutair AA, Singh RP (2016) Effect of Different Sterilization Methods on Biodegradation of Biomedical Polypropylene. J Environ Anal Toxicol 6:373. Doi: 10.4172/2161-0525.1000373, https://www.omicsonline.org/open- access/effect-of-different-sterilization-methods-on-biodegradation-of-biomedicalpolypropylene-2161-0525- 1000373.php?aid=73845

18. Materials

“Allergy proof bedding with the smallest pore size will always be all polyester. All cotton allergy-proof bedding will have a larger poresize but will still be an effective allergen barrier. Cotton/polyester blends are in the middle when it comes to pore sizes. Dust mite fecal matter and/or body parts (we don’t actually breathe in whole dust mites) are as large as 10 microns. Pet allergen and mold spores are about 3 microns. In order for a microfiber mattress encasing to be effective against dust mites, it needs a pore size of 10 microns or less.” https://allergystore.com/blogs/news/what-does-pore-size-mean-in-allergy-proof-bedding
Evaluation of materials used for bedding encasement: Effect of pore size in blocking cat and dust mite allergen.https://www.jacionline.org/article/S0091-6749(99)70495-1/fulltext
4 Pack Pillow Protectors Standard 20×26″ Hypoallergenic 100% Cotton Sateen Tight Weave 3-4 Micron Pore Size High Thread Count400 Style Zippered White Hotel Quality Non Noisy (4 Pack Standard Zip)
Opinion: Evolon is 1um, but has too much impedance to air flow to use as a mask (fails breathability)
Allergy Proof Bedding (Pore Size 1 to 6 micron, tested in some cases)

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The Big Four: Criteria for Fabric Mask Materials for COVID