## Which Fabrics Make the Most Effective Covid-19 Face Covering?

#### Measure How Much Air Flows Through Different Fabrics

©Travis Kelleher, Baylor College of Medicine.

• Length: Variable

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### Overview

Not all fabrics make equally protective face coverings or masks. The selection of material should not be left to chance. In this activity, students construct a mask tester to evaluate the filtering effectiveness of different fabrics.

### Teacher Background

The Science

The COVID-19 pandemic already has killed more than 1 million people around the world and caused illness in more than 35 million. At the beginning of the pandemic, scientists did not have enough evidence about whether masks would be effective against SARS-CoC-2, the virus that causes COVID-19. Now, growing evidence shows that wearing face coverings prevents spread of the virus.

N95 masks, which are used in medical settings, block about 90% of aerosols down to a size of 0.3µm. Most fabric masks can block more than 80% of aerosols of 4–5µm (See "Face Masks, what the data say." Nature News Feature, Oct 6, 2020, https://www.nature.com/articles/d41586-020-02801-8).

### Objectives and Standards

Students will test and evaluate the permeability of different fabrics and then reach conclusions about the suitability of different fabrics for use in face masks to protect against the spread of viruses and other microbes.

Science, Health, and Math Skills

Comparing/contrasting

Measuring

Interpreting

NGSS Science & Engineering Practices

Developing and using models

Planning and carrying our investigations

Using Mathematics and Computational thinking

### Materials and Setup

Materials for Science Investigation

The teacher will use a set of materials such as those listed below to create a demonstration anemometer. The teacher also will need a handheld fan, hairdryer set at the lowest speed, or sheet of cardboard for the demonstration.

Students will need the following materials:

• "Anemometer Assembly Instructions" (see accompanying student page)
• printed copies of the paper patterns and instructions for making the tester: parts 1 and 2
• sheet of cardboard, such from as a pizza or cereal box, approximately 8 in. x 10 in.
• glue, such as white school glue or a glue stick
• sharpened pencil
• tape, such as masking tape, painter’s tape, or clear plastic tape
• nail or pointed punch
• scissors
• a variety of test fabrics, such as a tee shirt, pillowcase, handkerchief, kitchen towel, bandana, or washcloth (it is not necessary to cut the fabric)
• handheld hairdryer (optional). If students will be testing their anemometers in the classroom or with other people, they will need to use a hairdryer set to “cool” and the lowest speed to test the various fabrics.

Setup and Teaching

Build an anemometer following the assembly instructions so that you can demonstrate its use to students. You’ll need a small fan or sheet of cardboard to create a breeze for the demonstration. To avoid having students breathing through various fabrics in the classroom, consider having students construct their anemometers at school but conduct the fabric tests as an assignment at home. Or, have students use a handheld hairdryer to test the fabrics in the classroom.

### Procedure and Extensions

Engage

• Begin the lesson by asking, Why is it important to wear face coverings during the COVID-19 pandemic? Accept all responses and discuss.
• Explain that the masks we wear during this pandemic and other disease outbreaks have two main functions. They protect the wearer from breathing in virus-laden moisture droplets, and they protect others from droplets breathed out by the wearer that may contain virus particles. COVID-19 is caused by a coronavirus called SARS-CoV-2. Unfortunately, symptoms of COVID-19 may not appear for 2 to 14 days, so a person may not know he or she has the virus. During that time, a person infected with the virus who does not wear a mask or take other precautions (such as careful hand washing or physical distancing) can unknowingly pass the infection to family, friends, and strangers.
• The virus particles are extremely small—far too tiny to be seen through the most powerful optical microscopes. Only advanced electron microscopes can image virus particles. Ask, If virus particles are so small, how can protective masks stop them? Accept responses and discuss.
• Explain that some virus particles “hitch a ride” on the tiny droplets of moisture expelled when an infected person talks, yells, sings, sneezes, or coughs. Except for very coarsely woven fabrics, the porosity (open spaces between threads) of many fabrics is large enough to allow air to pass through, but small enough to trap virus-laden moisture particles. But how do we know which fabrics are best for making masks?

Explore

• Tell students they will investigate the effectiveness of different fabrics for protective masks by using a “mask tester” they will construct.
• Show students your pre-assembled “mask tester.” Explain that this is an anemometer, a device used for measuring air movement. Anemometers are most commonly used to measure outdoor wind speed, but they also are used to measure air flow in air conditioning, gauge wind conditions for sports, check ventilation in mines, and other uses.
• Anemometers take many forms, including cups spinning around an axle, propeller blades, and electronic sensors. The anemometer used in this activity is one of the simplest forms.
• Use a handheld fan or hair dryer (or wave a small sheet of cardboard) with the anemometer to demonstrate how the needle moves on a pivot and swings upward when air flows by.
• Read the "Anemometer Assembly Instructions" page with students, and review the paper patterns to ensure students understand what to do. Using your model, point out how you (the teacher) assembled yours. Also demonstrate how to position the anemometer on a door.
• Before students begin construction, discuss their ideas for fabrics to test with the anemometer. Discuss possible options, such as a tee shirt (cotton knit fabric), old pillowcase, cloth handkerchief, kitchen towel, bandana, or washcloth. Students should ask permission before using any fabrics they find at home. It is not necessary to cut fabrics for testing.
• Instruct students to follow the procedure described on the "Anemometer Assembly Instructions" page. SAFETY NOTE: If students are conducting this activity in the classroom, have them use a hairdryer to test the fabrics. Otherwise, have them build the anemometer in class and test it at home with various fabrics.
• Remind them to record their results, including the material used and the anemometer measurements.
• In addition, have students devise a qualitative plan to evaluate and report (1) how well they were able to breathe through the fabric, and (2) how comfortable the fabrics felt on their faces.

Explain

• Upon completing the investigation, students will share and explain their results.
• Ask, Is it good or bad when the anemometer needle swings to the top of the protractor scale during a test? (Bad. The anemometer detects air movement, so the less the needle swings, the more effective the fabric is as a filtering barrier.)

• Ask, Were any fabrics good at blocking outgoing breath but difficult to breathe through?
• Follow up by asking, Which fabrics were most comfortable? Were they among the most effective? (People may not want to wear a mask made from a fabric that is scratchy or causes skin irritation.)
• Conclude with a class discussion based on the question, Combining everything you’ve learned in your investigation, which kinds of fabrics are best for making protective cloth face masks?

Extend