What Materials Can Block a Wi-Fi Signal?

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Have you ever suffered from poor Wi-Fi reception for your smartphone, tablet, or laptop? Certain materials can actually block a Wi-Fi signal; do you think that could be part of your problem? In this science project, you will do an experiment to find out which materials cause the biggest drop in signal strength from a wireless router.


Measure how much different materials affect the signal strength of a wireless router.


Odds are that you have probably accessed the Internet with a wireless device like a smartphone, tablet, or laptop. Have you ever been frustrated by a poor-quality or slow connection? In this science project, you will learn about one aspect of getting good reception: materials that can physically block Wi-Fi signals. Before you start, you will need to learn a little more background information about Wi-Fi.

Wi-Fi is the common name for a type of communication that allows electronic devices to exchange data or connect to the Internet wirelessly, meaning they do not need to connect to each other with cables. Wi-Fi devices do this using radio waves, which are a type of electromagnetic radiation. You are already very familiar with one type of electromagnetic radiation: visible light! Visible light and radio waves are just different parts of the electromagnetic spectrum (see Figure 1). Each part of the electromagnetic spectrum has a different frequency, or number of waves per second. Frequency is measured in hertz (Hz), so one hertz (1 Hz) is one cycle per second. Wi-Fi devices operate at either 2.4 or 5 gigahertz (GHz)Giga is the metric prefix for one billion (1,000,000,000, or 109).

Graph of the electromagnetic spectrum shows wavelengths next to images of scaled objects
Figure 1. A diagram explaining the electromagnetic spectrum. Each type of radiation has a different frequency. Humans are most familiar with visible light since that is what we can see with our eyes, but there are many other types of radiation, including radio waves, that we cannot see (image credit NASA, Wikimedia Commons users InductiveLoad and NI47).

Electromagnetic radiation can be attenuated, or weakened, when it passes through different materials. Think of visible light as an example. Some materials, like air or clear glass, let visible light pass through with hardly any attenuation at all. Other materials, like water or tinted glass, will only let some light through; and others like wood or metal will completely block visible light. Do you think the same thing applies to radio waves? Will some materials weaken or totally block radio waves, while other materials let them pass through? In this science project, you will find out by testing the ability of different materials to block Wi-Fi signals from your wireless router.

Technical NoteWireless signal strength is measured in units called Decibel-milliwatts, or dBm. Decibel-milliwatts are different from the regular metric units you are probably used to working with like meters, grams, and seconds. Decibel-milliwatts measure the power level of a signal relative to a base level of 1 milliwatt (mW), which is equal to 0 dBm. So, positive dBm values have a power greater than 1 mW, and negative dBm values have a power less than 1 mW. The dBm values you measure for this project will most likely be negative. It is important to note that a value that is closer to zero means a stronger signal than a value that is farther away from zero. For example, a signal strength of -15 dBm is a fairly strong signal, whereas a signal strength of -90 dBm is a very weak signal. For more detailed information about dBm, see the reference in the Bibliography.


  • What is the electromagnetic spectrum?
  • Which part of the electromagnetic spectrum does Wi-Fi use?
  • What materials do you think will block a Wi-Fi signal? What materials do you think will let a Wi-Fi signal pass through? (Hint: Look at some of the references in the Bibliography, and do your own background research).
  • What is a Decibel-milliwatt? Which is a stronger signal: -20 dBm or -80 dBm?

Materials and Equipment

  • Wireless router
  • Wi-Fi enabled device like a smartphone, tablet, laptop, or desktop with Wi-Fi adapter
  • Program or app to analyze the strength of the wireless signal (preferably in dBm). You will need to find one that works with your wireless device and operating system. Try searching for things like “wifi analyzer” or “wifi strength meter.”
  • Blocking materials to test. Note: While it may not be possible with all materials, ideally you should test sheets/pieces of material that are all approximately the same size. While it is obviously not possible to cut up steel or glass baking pans, you can use scissors or a utility knife to cut materials like aluminum foil, cardboard, or plastic so each test sheet is the same size. Some material suggestions include:
    • Aluminum foil
    • Steel baking pans
    • Glass baking pans
    • Cardboard
    • Plastic
    • Large container filled with water
    • Human body
  • Lab notebook

Experimental Procedure

  1. Make sure you do your background research and formulate a hypothesis about which materials will attenuate a Wi-Fi signal.
  2. Download and install an app or program for your wireless device that can measure the signal strength of a Wi-Fi connection. Some programs will provide a “signal quality” rating on a scale of 0–100, but ideally you should use a program that provides measurements in dBm. Ask an adult if you need help installing the program.
  3. Familiarize yourself with how to use the program before you start your experiment. Try walking around your house and using the program to take signal strength measurements in different locations. Do you understand how to read a measurement in dBm? Do you see changes in signal strength? Once you are comfortable using the program, move on to the next step.
  4. Create a data table like Table 1 in your lab notebook. You will use this to record your results.
Signal Strength (dBm)
Material Trial 1 Trial 2 Trial 3 Average Attenuation (dBm)
None (control)
Aluminum foil
Steel baking sheet
Human body

Table 1. Example data table. You can change or add rows to the table, depending on which materials you plan to test.

  1. Pick a location in which to place your wireless device for each test. It is important to keep this location consistent for each trial. Ideally, this location should:
    1. Be in the same room as your wireless router, several meters away from it.
    2. Be at the same height off the floor as your wireless router (i.e. this will change depending on whether your router is on the floor or on a table/desk).
    3. Not have any other barriers, like furniture or people, between your wireless device and the router.
    4. Allow you to see the screen of the wireless device (to take a signal strength reading) without standing in between the device and the router.
    5. It is also important to keep the orientation of your wireless device consistent between each trial. For example, do not rotate a smartphone from a horizontal to a vertical position between trials. Pick one orientation and keep it the same for each trial.
  2. Determine how you will arrange your test materials for each trial. The most important thing is to keep your setup the same for each trial of the experiment.
    1. Make sure the test materials are as close as possible to the router, without touching it. You do not want to accidentally bump the router, as moving it could cause a change in signal strength.
    2. You could have a volunteer stand off to the side (not in front of the router) and hold the materials up. Or, you could use textbooks, duct tape, or other household materials to hold the test materials up in front of the router. Remember to keep whatever support structures you use off to the side (just holding the edges of your test material) so they do not contribute to blocking the router’s signal.
    3. See Figure 2 for a diagram of an example experimental setup.
Diagram of a router and test material on one table and a person with a testing device on a separate table
Figure 2. An example diagram of an experimental setup. Notice the following key points: 1) The test material is close to the router, but not touching it, 2) the router and wireless device are at the same height, and 3) the person doing the experiment is not standing between the router and wireless device.
  1. Start out by measuring the signal strength with no blocking material. This is your experiment’s control. Measure the signal strength in dBm and enter this value under “Trial 1” in the first row of your data table. Repeat this two more times, for a total of three trials.
  2. Now, set up your first blocking material. Record three separate signal strength readings in your data table. Remember not to move the blocking material or wireless device in between trials.
  3. Repeat step 8 for each of your remaining blocking materials.
  4. For each blocking material (and your control case with no material), calculate an average signal strength in dBm and enter this value in your data table.
  5. Calculate the attenuation of the signal for each material by subtracting the signal strength with the material from the signal strength without the material (your control case), and enter this value in your data table. For example, say that for your control, you measured an average signal strength of -15 dBm, and for a certain material (we’ll call it Material A), you measured an average signal strength of -40 dBm. The attenuation for Material A would be (-15 dBm) – (-40 dBm) = 25 dBm. Be careful to keep track of the negative signs!
  6. Create a bar graph with material type on the horizontal line (x-axis) and attenuation in dBm on the vertical line (y-axis). Remember to label the axes of your graph. Which materials attenuated the Wi-Fi signal the most? The least? Do your results line up with your predictions based on your background research?


  • What happens if you use the same material for all of your tests, but vary its thickness? For example, use multiple sheets of aluminum foil or cardboard.
  • What happens if you use the same material for all of your tests, but vary its surface area? For example, squares of aluminum foil with sides that are 10 cm, 50 cm, or 100 cm long?
  • What happens if you test wet materials vs. dry materials (i.e. wet vs. dry cardboard)? What does this tell you about the impact of water on radio waves?
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