Finding and Selecting Polypropylene for Washable Masks

In this post we discuss how we think about selecting spunbond nonwoven polypropylene (NWPP) fabrics for washable masks, where we have found spunbond NWPP, and why we’ve chosen Smart-Fab® Double-Thick for our next round of testing.

Our Mission

Public Health Guidance on Polypropylene for Fabric Masks

• breathable
• water resistant
• durable/tear-resistant
• washable
• available by the yard/meter
• easy for sewists to source

Selecting Spunbond NWPP Sources

Unfortunately, the ideal spunbond NWPP mask materials have been hard to come by during this global crisis. Because data on commercially available materials is scarce and inconsistent, we have not been able to recommend a specific spunbond NWPP to sewists and makers.

However, sewists can evaluate the basic quality of NWPP sources by looking at how the material was originally intended to be used and existing industry and/or regulatory standards for those uses.

In general, industry standards suggest a hierarchy in the quality and manufacture of NWPP. For example, materials used for medical, food-contact, and textiles applications are typically required to meet minimum standards, whereas industry standards for disposable crafting and utility materials are less clear. 

• Medical NWPP: Medical-grade spunbond NWPP is being reserved for medical masks and is not generally available to sewists. The type of spunbond NWPP typically used in medical masks is lighter (~25 gsm) than the spunbond available to sewists (> 40 gsm) and is not designed to be washable or reusable.
• Food Contact NWPP: Materials designed to be in contact with food may be a good choice (e.g., reusable grocery bags) if medical grade materials are not available. However, they are not commonly available in bulk (i.e., by the yard or on the roll/bolt) for consumers.
• Clothing & Textiles NWPP: Spunbond NWPP is used in clothing, bedding, and other textiles. These materials are sometimes available by the yard, are frequently designed to be washable, and are designed to be safe for skin contact. 
• Crafting NWPP: Crafting NWPP is designed for crafting and classroom use but is not generally designed for reuse. Industry standards for the quality and manufacturing processes of crafting materials are unclear. However, some crafting materials are washable and manufactured following the same standards as other textiles. Crafting NWPP is widely available.
• Utility/Upholstery NWPP: Utility/Upholstery NWPP (e.g., cambric) is designed to be durable, but is not designed to be washed or worn. Industry standards for the quality and manufacturing processes are unclear. 
• Landscaping/ Geotextiles: NWPP used in Agriculture, Pond Liners, Geotextiles is frequently constructed with coarser fibers and has issues with particle shedding. It is not designed to be skin contacting, and it is generally considered not suitable for use in masks.

Finding Spunbond NWPP Sources for Mask Testing

Most medical-grade NWPP is currently reserved for medical use and not available to sewists for community masks, and the materials that are available are not usually washable. NWPP from reusable grocery bags, which is designed to be in contact with food, has been our top choice since early 2020 and was the focus of earlier testing efforts. However, the NWPP used in grocery bags isn’t commonly available by the yard/meter, and taking the bags apart to turn them into masks can be labor intensive.

• Upcycled Reusable Grocery Bags. Reusable NWPP grocery bags are designed to be washable, breathable, water resistant, and in contact with food (See “The Big Four” for more information). Mask fabrics constructed from three layers of upcycled NWPP have passed ASTM Level 2 fluid resistance and are breathability requirements. Avoid previously used/worn/soiled materials. Avoid materials that are highly embossed/decorated because they might not be breathable, and may not stand up well to re-use.

Since medical and food-contact safe NWPP options are not readily available to sewists by the yard, we have focused on investigating the spunbond NWPP used in clothing, textiles, crafting, and upholstery applications for our next round of testing. 

The table below summarizes common spunbond NWPP sourcing options.

Smart-Fab® Double-Thick is Our Choice for Testing

Based on feedback from sewists, conversations with manufacturers and distributors, ease of online purchase, a review of the literature, and informal testing/evaluation of spunbond NWPP materials, we have selected Smart-Fab® Opaque (Double-Thick) for further investigation and formal laboratory testing and have prioritized getting this material to the lab as early as we can in 2021. (Thank you to all who have donated to make this possible!)

Smart-Fab® Opaque Double-Thick Rolls

The Smart-Fab® Opaque Double-Thick is a midweight (67 gsm; 2.0 oz/yd2) crafting NWPP frequently used as a background material for bulletin boards. According to the manufacturer, Smart-Fab® Opaque (Double-Thick) is made from 100% virgin polypropylene and has been manufactured with quality and cleanliness controls consistent with clothing & textiles industry standards. For example, Smart-Fab was tested and approved to be compatible with the Fire Flammability Act Standard (16 CFR, part 1610) per the Consumer Product Safety Commission directive (report on file). According to Smart-Fab’s FAQ “In practical terms, it means that Smart-Fab is safe for usage in all the applications mentioned on our website, including in close proximity to children (e.g. in classrooms, for Halloween costumes, etc).”

• Washing: Feedback from sewists suggests that it is washable, which is confirmed by the FAQ on the manufacturers website.
• Availability: Smart-Fab is widely available in the U.S., Canada, and Australia (in the U.S,. it is available by the roll through Amazon, Walmart, and some craft stores like Dick Blick, which sells 48 inch by 24 foot rolls for $19.78 US).
• Testing: Recently published literature suggests that 3 layers of Smart-Fab® provide decent filtration in fabric masks (Long et al, 2020). Smart-Fab double-thick should pass the “light” test sewists are familiar with for cotton fabrics.
• Water-Resistance: DIY testing suggests that it is water resistant, but not as water resistant as the upcycled NWPP bags evaluated. 
• Nota: The Smart-Fab website states that Smart-Fab is food contact safe; however, this only applies to the “Smart-Fab Dairy” materials, and not to the Smart-Fab crafting materials.

Other Spunbond NWPP Sources

Cambric NWPP (e.g., Pellon 915)

Cambric NWPP is typically a lightweight (50 gsm; 1.5 oz/yd2) utility/upholstery NWPP that is frequently black in color. It is commonly used as a dust cover, especially for use under mattresses and other furniture items. If using a 50 gsm cambric, consider including at least one extra NWPP layer. This material is significantly lighter weight than the Smart-Fab Double-Thick and has a lighter/softer hand. 

• Washing: Directions from the supplier say cambric should be spot cleaned. However, feedback from sewists suggests that it can be washed and reused. In addition, the Denver Mask Task Force has verified that the Pellon Cambric 915 can withstand sterilization in their autoclaves.
• Availability: Cambric (black in color) is commonly available with the same specifications from three distributors in the U.S.: Pellon Cambric 915; DreamCraft LLC Cambric/Upholstery; and Dritz (Prym) Cambric/Upholstery.
• Water-Resistance: In DIY water resistance tests it performed similarly to Smart-Fab Double-thick.

Sailrite Pillow Protector NWPP

Sailrite Pillow Protector NWPP material is a lightweight (40 gsm;1.2 oz/yd2) textile/upholstery NWPP that is marketed for use as a reusable pillow covering material. If using Sailrite spunbond NWPP, consider using one or two extra layers of the NWPP.  If using this, or other lightweight NWPP materials, consider using 2 or 3 layers wherever 1 layer of a heavier NWPP is recommended.  

• Washing: The material provider (Sailrite) suggests this material can be washed and reused up to 5 times.
• Availability: Pillow-protector NWPP is available online from Sailrite
• Testing: The manufacturers provide some ASTM testing information for it (ASTM D 5034-09), though not information commonly used by mask makers.
• Water-Resistance: DIY testing suggests that it isn’t as water resistant as some of the other spunbond NWPP materials.

Oly-Fun NWPP

Oly-Fun is a midweight ( 65 gsm;1.9 oz/yd2) crafting NWPP. Oly-Fun feels more plastic-y than Smart-Fab and is stiffer and harder to work with/sew.

• Washing: Joann’s fabrics provides the following washing instructions for Oly-fun “Care: Machine wash on gentle cycle and air dry; an iron may be used, but do so carefully on a cool or low setting with a pressing cloth”, however the manufacturer says that it should be considered a disposable single use material.
• Availability: Oly-Fun is commonly available by the yard through Amazon, Walmart, and Joann’s fabrics.
• Testing: Published literature suggests Oly-Fun can be used as a barrier in masks (Lustig et al, 2020).  
• Water Resistance: DIY testing suggests that it is more water resistant than the Smart-Fab

Sew-In NWPP Interfacing

Sew-In NWPP interfacing is a textiles/clothing NWPP that may be available in lightweight, midweight, and heavyweight options. We are still looking for consistent, reliable, and available sources of materials and feedback from sewists. Availability by the yard varies significantly by region, and within the US, most of the sew-in interfacing available is made from polyester and not polypropylene. If using lightweight NWPP interfacing considering adding one or two extra NWPP layers. For information about Pellon 915, see the section on black cambric utility/upholstery NWPP.

• Washing: Sew-In NWPP Interfacing is generally considered washable.
• Availability: We’re heard good things about 70 gsm spunbond NWPP sew-in interfacing available to sewists at local shops and chains in Canada (e.g., Fabricland), but have not been able to source it online and for U.S. audiences.
• Testing: The WHO guidance on fabric masks, and Zhou et al, 2020 suggest interfacing may have a good balance of filtration and breathability. 
• Caution:  If using interfacing, avoid fusing interfacing as the glues and adhesives may reduce the breathability of the fabric and have unknown inhalation risks.

Sterilization Wrap (Medical NWPP)

Although rarely available to sewists by the yard, some types of 100% NWPP sterilization wrap may be suitable for use in masks. If considering sourcing medical NWPP, avoid heavy duty sterilization wrap that is not sufficiently breathable and take care with materials that are not washable (SMS wrap). Avoid materials with surface treatments that improve water resistance, but reduce breathability and may introduce inhalation risks. It is important to note that most sterilization wrap is a combination of spunbond-meltblown-spunbond (SMS) NWPP, which may not be washable.

• Washing: Not usually washable
• Availability: Generally available for hospital use, but not usually commercially available to sewists and community members.
• Testing: A couple of studies have looked into the breathability of sterilization wrap and found that heavy duty sterilization wrap (e.g., H600) has decent performance on filtration, but it isn’t sufficiently breathable [Grigg et al, 2020; Sousan et al, 2020].  They suggest lighter weight sterilization wrap (e.g., H100 or H300) might be a better choice.

For More Information About Polypropylene in Masks Check Out:

• The MakerMask FAQ: Questions About Polypropylene
• The Big Four: Criteria For Community Mask Materials
• Mask Fabrics: Introduction to Fibers and Fabrics

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