MakerMask

FAQ

An image of the MakerMask: Origami showing water beading up on the surface of the spunbond nonwoven polypropylene (NWPP) mask material

In this FAQ we answer questions about reusable fabric masks (nonmedical masks), including questions about mask fabrics, nonwoven polypropylene (NWPP), and mask designs. Some of the key questions answered in this FAQ are:

Questions About Polypropylene

What is polypropylene?

Polypropylene (PP) is a lightweight synthetic material that is inexpensive, durable, breathable, water resistant, and recyclable (#5). PP is generally considered non-toxic, and safe for human contact. PP is used in a broad range of applications and is available in many forms. For example, PP is available as sheets of plastic (e.g., in yogurt containers), as woven fabrics (e.g., in clothing), and as nonwoven fabrics (e.g., in masks). The type of polypropylene used in masks in nonwoven polypropylene (NWPP).

Is polypropylene safe?

Yes, polypropylene is nontoxic and is generally considered the safest plastic for human use. However, as with all textiles, there are different thicknesses and grades of NWPP and we cannot guarantee or vouch for the effectiveness of hand-made masks constructed from alternatively sourced materials. For more information to help guide your selection of polypropylene materials for community masks read more at: “The Big 4: Criteria for Community Mask Materials.” 

Why is nonwoven polypropylene used in masks?

Nonwoven polypropylene is used in masks because it is nontoxic, breathable, hydrophobic (water-resistant), lightweight, provides filtration, and is inexpensive.

An image of the MakerMask: Origami showing water beading up on the surface of the spunbond nonwoven polypropylene (NWPP) mask material
Hydrophobic spunbond nonwoven polypropylene (NWPP) used in the MakerMask: Origami.

What is nonwoven polypropylene?

Nonwoven polypropylene (NWPP) is the most common material used in medical grade masks. Instead of being woven like cloth, NWPP is created by spinning polypropylene fibers into threads and laying them down in a porous web that is breathable, provides filtration, and is naturally water resistant. There are two different types of NWPP that are used in masks: spunbond NWPP and meltblown NWPP.

What is the difference between spunbond and meltblown NWPP?

Spunbond NWPP is washable and reusable where meltblown NWPP is considered a single-use (disposable) material. This is because of structural differences in the materials and how they are manufactured. For reusable fabric masks we recommend spunbond NWPP. For a deeper dive into the differences between spunbond and meltblown NWPP, see: “Mask Fabrics: Introduction to Fibers and Fabrics”

  • Spunbond NWPP is a sturdier material spun from larger diameter fibers that are thermally bonded together, which makes them more suitable for washing and reuse. 
  • Meltblown NWPP is constructed from smaller, more delicate fibers, resulting in a material that is not generally considered washable or reusable. Although meltblown NWPP is considered safe in commercially manufactured masks and filter inserts, the size of meltblown fibers suggests extra caution may be warranted when cutting, handling, and/or sewing these materials due to potential inhalation risks. 

The construction of NWPP showing how it is spun into a fibrous web and then thermally bonded to create the spunbond texture

Is spunbond polypropylene good for reusable face masks?

Yes. Spunbond NWPP is considered a good choice for fabric masks because it is lightweight, reusable, breathable, water-resistant, and helps with filtration. However, meltblown NWPP is not considered washable and should not be sewn into reusable masks. For more on how to identify and select NWPP for masks see: “The Big Four: Criteria for Fabric Mask Materials for COVID

Infographic showing some of the key characteristics of spunbond nonwoven polypropylene (NWPP) for masks

Is all spunbond NWPP the same?

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 constructed from alternatively sourced materials. For reusable fabric masks we recommend using spunbond NWPP because it is washable and reusable.

How do I evaluate whether my nonwoven polypropylene will work for a mask?

First, check to make sure that the fabric is made from 100% polypropylene (look for a label or tag). Next, look for the dimpled texture characteristic of spunbond nonwoven fabrics. To check that it is water resistant, 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. 

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

What about sew-in vs. fusible (iron on) interfacing?

If NWPP interfacing is used, “sew in” interfacing is preferred to “fusible” (iron on) because: 1) the plastics beads used in iron-on interfacing may reduce the breathability of the material and 2) the types of adhesives and binders used in the “dots” in fusible interfacing may are not have been evaluated for potential inhalation risks associated with use in masks. For more information fusing interfacing check out the following links:

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 suggests poor filtration performance, and they are not always water resistant.

What about surgical barrier materials?

Nonwovens used as barriers in other medical applications (e.g., gowns and surgical drapes) may contain coatings or chemical treatments to enhance water-resistance and water-repellence. 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).

Where can nonwoven polypropylene be purchased?

Spunbond nonwoven polypropylene can be upcycled from a number of different places, and can be found in bulk (i.e., by the yard) as sewing and/or crafting material. Specifics about where to buy NWPP vary regionally. Click here for our guide to “Finding and Selecting Polypropylene for Washable Masks

Polypropylene: How to Choose? (image) Shows a stick figure leaning against a big question mark with detailed image of spunbond nonwoven polypropylene in the background

Questions About Reuse, Cleaning, and Disinfection

Are nonwoven polypropylene masks reusable?

Yes, fabric masks made from spunbond nonwoven polypropylene can be washed and reused (by the same individual). Disposable medical masks (and respirators) that contain meltblown NWPP are designed to be safely discarded after a single use, but due to ongoing shortages may be reused up to five times when safely stored (e.g., in a breathable paper bag) for at least 5 days between uses [CDC, 2020]. 

Infographic talking about cleaning vs disinfecting polypropylene masks

Can nonwoven polypropylene be washed?

Yes, spunbond NWPP can be washed. Check for specific washing instructions from the mask and or material manufacturer. In general:

  • NWPP can be hand washed in warm or hot water, rinsed thoroughly, and hung to dry. Handwashing may extend the longevity of NWPP materials.
  • NWPP can be machine washed (warm) and tumble dried (low). We recommend putting NWPP masks in lingerie bags while washing to help them retain their shape. 

For disinfection, spunbond NWPP masks may be boiled for 10 minutes and then hung to dry. Avoid using bleach or alcohol on these fabrics, because those chemicals break down the properties that make NWPP a good choice.

Is nonwoven polypropylene recyclable?

Yes. NWPP is recyclable (look for recycling #5). Check with local and regional recycling policies for details. In addition, the spunbond NWPP used in fabric masks can be washed and reused, which helps cut down on waste.

Illustration of the Earth wearing a mask and carrying a reusable nonwoven polypropylene bag

Questions About Mask Layering and Construction

How many layers should my mask include?

Best practices currently suggest that fabric masks should be constructed of three or more layers of breathable fabrics [WHO, 2020]. For more information about the WHO Guidance on Fabric Masks (last updated December, 2020) check out: WHO Fabric Mask Guidance – December Updates

Key points from the December WHO Guidance on Fabric Masks including nonwoven polypropylene

What fabrics and layers should be used for each layer?

In general, the materials considered best for use in reusable fabric masks are water-resistant nonwoven fabrics (e.g., NWPP) and tightly woven cotton fabrics. For general use, MakerMask typically recommends either 3 layers of NWPP (NWPP-NWPP-NWPP), or a skin-contacting layer a hydrophilic fabric (e.g., cotton) with 2 outermost layers of NWPP (cotton-NWPP-NWPP). The NWPP layers are designed to act as barriers to droplets, which help contain the users droplets and help protect the user by preventing outside droplets from penetrating the mask [Songer, 2020]. For more information see,

Can I use cotton as the outermost mask layer?

We recommend using NWPP as the outermost mask layer due to its water resistance and hydrophobic properties. If a cotton layer is included, using it as the innermost mask layer (closest to the skin) to absorb the users droplets is preferred [WHO, 2020]. For more information, see:

Should I iron NWPP masks? What about while I’m making the folds?

NWPP has been known to melt with some irons and could damage both the mask and your iron. For this reason, we do not recommend ironing.  If you do decide to iron your masks, use precautions for sensitive/delicate fabrics such as ironing on the lowest heat setting and placing a towel or other cloth between the mask and your iron.

What is GSM and how is it calculated?

Both woven and nonwoven fabrics can be characterized by ‘fabric weight’ in terms of grams per square meter (gsm) or ounces per square yard (oz/yd²). Although we use gsm throughout our discussions, depending on where you are, oz/yd² may be used. It is easy to convert from one to the other by googling it, or using an online conversion tool such as this “Textile and Fabric Weight Converter”.

We use gsm to describe fabrics because it can be used to describe both woven and nonwoven fabrics and it can be easily measured by scientists and home sewists alike. All you need is a kitchen scale and a ruler!

Calculation of gsm from one yard of mask fabric

How can I measure the GSM of my fabrics (cotton and NWPP) at home?

If the gsm (grams per square meter) of a given fabric is not provided by the manufacturer, it can be calculated at home using a digital kitchen scale, a ruler, and either a calculator following these three easy steps:

  1. Measure the length and width of your fabric in meters (or convert to meters; e.g., 1 cm = 0.01 m, 1 inch = 0.025 m, or 1 yard = 0.9 m). 
  2. Weigh your fabric on a kitchen scale in grams (or convert to grams; e.g., 1 ounce = 28 grams). 
  3. Calculate the gsm of the fabric using the formula below:

GSM = Fabric Weight / (Length x Width)

 

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