Introduction: Mask Reborn Box: New Life for Old Masks

About: This is Kalimov. Come from Macao and base in Shanghai now. People may think I'm a weird person. Well, one of my motto is below. Hope for hopeless, and hopelessness for hope. Creative comes from it.
  • We created an affordable, at-home kit to extend the life of masks so you can join the fight against the pandemic by helping your community.

It's nearly five months since the idea of renewing used masks was born. Today, though in several countries COVID-19 seems not to be serious, most of the world is still suffering not only from the bodies, and also the society structure. Here I refer some records from our project site, Mask Aid Project, to tell you why we started it.

The Mask Aid Project team:

Kalimov Lok

Jason Leong

Torrey Nommesen

John Lee

Daniel Feng

Halima Ouatab

Thanks to Dr. Jian-Feng Chen, the Academician of Chinese Engineering Academic, and his team members. We based our process on their report of how to safely reuse disposable masks. This is the same progress used by the National Center for Biotechnology Information.(See Pic 2)

Experts from Reuse of N95 Masks white paper by Dana Mackenzie featuring research from Professor Jian-Feng Chen and colleagues at Beijing University of Chemical TechnologyAnother useful source of information that helped us to validate our process is the Stanford white paper Can N95 respirators be reused after disinfection? And for how many times? by Lei Liao, Wang Xiao, Mervin Zhao, Xuanze Yu.

Thanks to my teammate, Torrey Nommesen. Without his correction of gramma and expressing ways, I couldn't share the whole stuff in a native English speaker way.

If you want to read "how to build" first, you may skip this part and jump to the material part.

An Idea Is Born

Kalimov Lok (Referred from

When my country declared an emergency, I had a bad feeling that I couldn’t put my finger on. I couldn’t really wrap my head around it at that time – I was in a fog. It was January 23rd, 2020.

The next day, my mother came to Shanghai from Hungary to celebrate the Spring Festival with me. When I picked up her at the Pudong Airport, she had a face mask on. The next day, we heard that there was a quarantine imposed by the government. My mother was a biology teacher in Macao so she realized that the situation could become serious very quickly because Macao has the highest population density in the world. She also knew that it would be very difficult to determine who carried the virus unless they were diagnosed. Wearing a mask was not only to protect ourselves but also for the safety of others. So she went back to Macao two days later to get about 70 masks for me. She bought them in Hungary, but they were marked ‘Made in China.’ Thanks to my mother, I was able to obey the laws in China and go outdoors during the quarantine with a mask on. Later, I was able to use these masks for testing.

As people were staying home for much longer periods than before, they were learning a lot about the virus from TV and the internet. It slowly dawned on me what the bad feeling I had earlier was all about: even though there were more people in China infected than anywhere else, it would soon become a worldwide pandemic. China is the biggest face mask manufacturer in the world, and most of them are made in Xiantao, a city right next to Wuhan. The world’s mask supply was coming from ground zero of the epidemic.

People started asking, ‘How hard could it be to make mask?’ We soon found out: a machine can sew a mask in half a second, but it takes a week or sometimes up to to half a month for them to be ready for use. The masks need to be sterilized by epoxy ethane gas and then the mask needs to be naturally aired out before packaging for shipment. While waiting for the masks to be made, people were on their own. It became clear that in the very best scenario, it would be Valentine’s Day before any new masks were available.

I calculated how many masks the Chinese people would need. Later, I needed to refactor as it became a global pandemic. I was shocked. By my calculations, we needed to produce over 500 million masks a day! I think this was a major reason for the government wanted to warm people that they needed to stay home. I’m pleased to note that most people in China did stay home.

But we need to go outside to survive. We need to go outside to buy food, and when we go outside, we need to wear a mask. But if masks are in short supply, what can we do? Some people tried to boil disposal masks, or spray alcohol on them to disinfect them. Medical professionals warned us that this can ruin a mask. This is fine for an ordinary cloth mask, but it doesn’t work for N95 or PM2.5 masks. An N95 mask blocks the virus not only because of the density of its filter but it also needs to be statically charged to capture particles. Not many people knew this before this pandemic. Using alcohol dissolves the middle layer, and hot water removes the static electricity needed to make the mask useful. The only acceptable way to sanitize a mask is to apply a UVC light or hot, dry air. This way it doesn’t damage the mask as much because it doesn’t remove the static charge while the masks are being disinfected. The electricity will still dissipate after a day or two, but it’s still better protection than not sanitizing at all.

So could we find a way to recharge a mask? If we could get them disinfected and recharged, they could be at least 90% renewed. The more people that did this, the less of a shortage and panic we could have during the first stages of a pandemic.

I started to research the possibility of making a tiny factory at home and I had an insight. An ordinary factory uses epoxy ethane after the mask is sewn because it is more efficient given the number of masks they produce. They cannot sterilize the cloth before they sew it because the machines would pollute the mask. However, for home use, production volume would not be a factor. Perhaps we can completely sanitize a used mask without worrying about removing the static electricity and then recharge it later.

I checked the price of high-voltage static electricity charging machines and was disappointed. The only ones I could find were for industrial use. Besides being too large, the price of the available units were getting more and more expensive because factories needed them to produce more masks. I’m was sure there was another solution besides bringing a full-scale mask into the home or into a community center. I needed to make it portable, or at least desktop-sized, and I needed to make it affordable so people could turn their places into tiny factories and come to rescue in the early stages of a pandemic.

So I got an international team together to help me. I, Kalimov Lok, am doing the principle experiments and making the prototype. Jason Liang, PVCBOT maker, is trapped in Yichang, Hubei, near Wuhan, so he is doing market research and experimentation. Torrey Nommesen is an American currently quarantined in South Africa, and is making our web site and helping with English language press for our project. Daniel Feng, an industrial designer in Guangzhou, will work on finalizing the design for production once the prototype is built. John Lee, a professor in Zhongshan, is helping us with production and manufacturing. We have been working since March. We will post our progress online at if you are interested in following our journey


Hardware components

  1. high-voltage booster DC 5V input and 400KV output × 1
  2. LM2596 module DC-DC 12V/5V regulator × 2
  3. Switching power supply AC 110/220V DC 12V 100 watts × 1
  4. Switching power supply AC 110/220V DC 5V 3.5 watts × 1
  5. DC Fan DC 12V 0.6A × 1
  6. PTC Heater AC 220V 300 watts × 1. You can change to AC 110V depend on where you live.
  7. DHT11 Temperature & Humidity Sensor × 1
  8. relay DC 5V control, 4 connectors × 6
  9. SS14 diode SMD package × 7
  10. S8050 triode SOT-23 package × 6
  11. 0603 LED 0603 SMD package × 6
  12. 300 ohm resistor 0805 SMD package × 6
  13. 10K ohm resistor 0603 SMD package × 6
  14. Capacitor, 220 µF SMD package × 1
  15. Capacitor, 470 µF SMD package × 1
  16. Capacitor 1000 uF SMD package × 1
  17. Capacitor 22 uF 0402 SMD package × 2
  18. XH2.54 2P socket × 6
  19. XH2.54 3P socket × 2
  20. XH2.54 4P socket × 1
  21. XH2.54 2P wire × 6. 5 are single header, 1 is double header.
  22. XH2.54 3P wire × 1
  23. XH2.54 4P wire double header × 1
  24. Switch Button × 5PH2.0 2P socket × 6
  25. PH2.0 2P wire single header × 6
  26. KF-235 Spring terminal × 8
  27. UVC light tube(wavelength shorter than 285nm) × 2
  28. UVC light tube driver(supports 2 tubes on 1 driver) × 1
  29. 5.6M ohm high voltage resistor × 1
  30. 1 ohm 5 watts cement resistor × 1
  31. OLED 128*64 resolution, IIC interface × 1
  32. LGT8F328P MCU board × 1.Arduino nano compatible board and I use Arduino IDE to program it. This needs board library. You may use ordinary arduino nano instead of it.
  33. Carbon fiber non-woven × 1 large piece
  34. Aluminum foil × 1 (big size)
  35. dual adhesive tape (big size). You can use some duct tape instead.
  36. Some foam tape
  37. Plastic net
  38. Velcro
  39. a small piece of strong magnet
  40. Reed Switch, SPST-NO × 1
  41. Wire Clip × 20
  42. 2.54 pin socket(15P) × 2
  43. 3P wire(60~80cm long) × 1
  44. Plastic Angles Bar 6 meters long
  45. Triangle plastic angle × 4
  46. AC socket AC-01 × 1
  47. Mains Power Cord, 14 AWG × 1
  48. 18 AWG wire about 1 meter
  49. 5.08mm pitch pin ×2, 1 is 2P, another is 3P.
  50. PP hollow board × 5. 50*50cm size, 5mm thickness
  51. PC hollow board × 3. The structure inside the board is better to be hive like. 50*50cm size, 12mm thickness.
  52. Submerge pump × 1. With rubber tube.
  53. Thermostat Switch × 1. React temperature 100/70 degrees celcius.
  54. ESD Protection Device ESD5B5.0ST1G × 30. Protect the controlling board not to be shocked by static charge.

Software tools

Arduino IDE,


Hand tools and fabrication machines

Soldering iron

Solder Wire, Lead Free

Wire Stripper & Cutter, 30-10 AWG Solid & Stranded Wires

paper cutter

Laser cutter

Electrostatic meter(It is used to measure the remained surface static charge.)

Step 1: Before Building, Let's See Some Facts

Factors that affect the protection of masks

Filtration pore size - Because of the size of the microscopic holes in masks, air flows but water droplets and particles of dust are blocked. But the can only protect for a few hours before they are blocked and are no longer breathable.

Material - N95 masks are made using what's called electret melt-blown nonwoven. When melt-blown is made, it needs to be charged. But if you clean these masks with alcohol or disinfectant, it ruins the fiber. Clean water doesn't damage melt-blown but it does draw out the remaining electrostatic charge.

Static charge - Tiny particles of the scale known as PM2.5 or PM0.3 can fit through the pores in the fabric. To stop these particles, an electrostatic charge is applied to the non-woven melt-blown layer of medical masks. The static charge attracts tiny particles like smog, bacteria, and viruses so they attach to the fiber while still allowing airflow. This is the difference between medical masks and normal cloth masks. However, water vapor that comes from normal air humidity, our breath, and our sweet can draw away the charge. That's one of the reasons why experts tell us to change our masks every 4 hours.

What is our process?

1. We wash used masks or N95 respirators gently without detergent. This removes dirt, sweat, and the remaining charge on them.

2. We dry masks with 56~70ºC air for 30 minutes. This is base on science articles that show that COVID-19 is eliminated above 56ºC.

3. We also apply UVC light either at the same time or after the drying process.

4. We recharge the masks with a high-voltage electric field. This is the main purpose of our machine. We want to scale down an industrial electret machine to a desktop size so that every family or community center can recharge their masks.

Why can't mask factories just make more masks?

Well, let me tell you a true story that happened in China. The government warned people not to buy those any new masks before February 14th. The reason is that although each mask takes only half a second to be sewed and then 4 or 5 hours to be sterilized, it takes up to 2 weeks for the sterilizing vapors to dissipate and be safe to use. This is because they use ethylene oxide vapor which needs time for the toxic gas to dissipate before being sold.

It is hard for factories to change their process quickly as they are designed for mass-production. They don't use hot water washing as it draws out the charge. They don't use hot air or UVC treatment as it takes space and new equipment to do. They use ethylene oxide vapor because it doesn't affect the charge but it eliminates bacteria contaminates during production. It's more efficient and lowers the cost to produce masks. In this crisis, 15 days of waiting for us feels like 15 years. Since you don't need the scale of a factory, we can scale down the huge machines that they would use. Since we can re-apply the static charge, we don't need to worry about losing the charge while we are sanitizing. And we don't need to horde masks because they can be renewed again and again.

Before building, let's see some facts

In Pic 1, it was an old mask. I used a static meter to check it. It's nearly useless. The static charge was low.

In Pic 2, a new mask should have static like this. I made an experiment of recharging. You can download the raw video attachment.

From Pic 3, you can see the result of a recharged disposal mask. And it's amazing that recharged mask could have much stronger static charge than a new one! In my opinion, it was due to the process of mask manufacturing. Two weeks delay before shipping out, and to the final users, this can weaken the static charge on masks.

Step 2: Enclosure Design

I built the prototype with PP hollow boards as they are light and waterproof. However, due to the hot air that may soften the boards inside, I made the three floors in the middle with PC hollow boards. You don't have to worry about the enclosure outside as the boards can be cooled by outside air.

Below I show you the size you are going to prepare. Paper cutter is sharp enough to cut PP boards. You can use laser cutter if you want to be neat and faster.

First, we need PP hollow boards. They are 5mm thick.

Yellow and black parts are jplastic angles and triangles.

The forth picture is the control & display panel. The size of the holes depends on the OLED and buttons. (The final one has five round holes instead of the 4 pictures above as my teammate strongly suggested a reset button)

In Pic 5, this plate holds the position of plastic net, which contains masks inside.

Pic 6 shows what PC hollow board looks like. It's strong and it is rated to survive 100ºC heat. In reality, it can actually exceed the 100º C specification. It is thicker than the PP hollow board we used and is about 12mm thick. We need 3 45 x 45cm pieces.

There is a PP drawer, used for being washing tanks. In this size, we can put 6 masks inside it. Of course you can put more as surgical masks are thin. For N95 respirators, you'd better use plastic net mentioned steps later to squeeze them to save space. Don't worry, squeezing N95 respirators won't hurt fibers on them.

I used 3D printed plastic angle bars instead of ones I found later on the internet while we were participating in the MIT Hackathon Challenge "Africa Takes on COVID-19". Using real plastic angles will be cheaper but it takes time to get.

Then I placed PC hive boards on each layer's floor. These boards were stronger than PP hollow boards and can withstand hot air without having to worry about structural integrity. However, it’s more expensive so I only used 3 pieces, each 45 x 45cm and 12mm thick. The PP boards shown earlier work fine for the outside of the box because they can keep their strength since they are exposed to cooler air outside the box.

Step 3: How Does the Static Recharge Work?

The main principle of our box is that it renews masks because of electrostatic recharging. I basically built a scaled-down electret machine. This is the origin of the Mask Aid Project idea. As melt-blown fibers were scarce in the first stage of the outbreak, some people started thinking about how to reuse disposal masks. We experimented with many ways to recharge static on old disposal masks. There re too many to mention here, so I will focus on the final result. (Check out our story on the Mask Aid Project website if you are curious.)

The first picture shows how the middle layer material of masks is made in a factory: the voltage of the machine reaches about 120 kilovolts. Through a process called dielectric breakdown, the fiber in the middle of the capacitor like structure becomes charged. It is not technically a complete breakdown though because there can't be any sparks or the machine could burn the fiber. As an aside, a key part of the process is the use of an "electro-corona, " so we privately joke that we are fighting “Corona vs Corona”.

Since we are talking about high-voltage, some may worry about its safety. First, you are not going to touch it. Second, we can’t have expensive, powerful, gigantic machines sitting in our living room. Third, Joule’s Law is amazing! We boost 5V to 400KV so the current is too low to be fatal. Tasers are much more dangerous.

Electro-corona is a happy medium between complete dialectic breakdown and an open circuit. Using Ohm’s Law and some data I found online, I selected a high-voltage resistor of about 5 or 6 million ohms. This can controls the current while preventing sparks. The second picture shows what high-voltage resistors look like.

The third picture is a high-voltage generator. The red and green wires are the positive and negative inputs. You need a static meter to find out the output charge. It's cheap and you can scarvage a lot.(Tasers, mosquito killers) However, from the COVID-19 crisis, I learned that it's bloody expensive in US and Europe. Most of them are imported from China and they are really cheap. (A funny fact that it is used to drive animals back to home by farmers in China.)

When it’s on, its body becomes hot as it creates a near short circuit. The module was not designed to work this way. It was designed to work for only a few seconds at a time. We needed it to work continuously so we hacked it.

We put a 1-ohm ceramic resistor between the power and the positive input.

As a result, the modification to the circuit will be the last picture.

Step 4: Building Discharge Poles

At the beginning of the outbreak, I was exploring options for the materials I could use in my prototypes. The parts could not be restricted or too expensive. One frustration came with the discharging brushes available on the market. They were effective, but they made with carbon fiber so they were expensive. Also, due to the heightened need for mask making machines, their price was about 50 times normal.

So I had to change my perspective. People working in the IC chip industry are very concerned about static as it could spoil the product. They use many ways to protect from a static charge. The material they use as a conductor is not as good as metal, but it draws out static charge continuously. We found the material to be much more affordable if you know how to hack them. You can find this material in the B.O.M. list of this instructable.

I made two discharge boards (one is black because I ran out of my white duct tape). Finally, I buried wire beneath them as connection.

Step 5: Building the Hot Air Fan Module

Why not use a hairdryer instead? In the beginning, experts did suggest that we should use hairdryers to sanitize masks. However, they also noticed people shouldn't use them for too long as it could damage the dryers. Also, a lot of people are not patient enough to hold a hairdryer for half an hour. Also, temperature control on hairdryers is not that accurate. Once it overheats, the air could melt disposal masks.

So we built one showed in Picture 1. Heating such a big layer would take too much power. We chose a PTC heater like the kind you find in AC units. We combine it with a DC brush-less fan, which was quite powerful at 12V 0.6A.I used some screws to attach PTC on the fan, that Picture 2 shows the detail.

We had two ways of controlling the temperature: One by soldering a thermostat switch on the PTC, another by using a DHT11 sensor to tell the MCU when to shut the heating unit down. I used both of them.

Step 6: UVC Treatment

UVC radiation kills bacteria and viruses. Many people know about this technology. The problem is that few people know the difference between UVA, UVB, and UVC. Some think that they are the same. That’s why there were fake UVC lights on the market when the outbreak began. In our project, we only trust UVC, unlike the kind of light that nail polishing machines use.

Here again, I faced some hard choices. We knew there were three ways to make UVC, the most common being hot cathode (HCFL), rarer is cold cathode (CCFL), and then there is UVC LED. For the environment and for shipping, it originally seemed that UVC LED was the best choice. But - we finally chose CCFL for many reasons. Like I have said before, we didn’t want parts that restricted or overpriced. A lot of research went into how we settled on CCFL.

I installed two tubes in the box, one on the floor of the middle layer, and another on the ceiling. I stuck some wire clips to hold the tubes.

The cold cathode UVC tubes and driver board were low cost but still powerful. They run at 12V and consume 10 watts total power. A scientific paper said that 15 minutes UVC exposure to surfaces can kill almost all bacteria. We decided it was good to pair it with hot air.

P.S. The origin wire on the tubes were too short, so we need to cut and solder longer wires to extend them.

Step 7: Washing Function

You may ask, why wash the mask if it would clear all remain static charge?

Washing is optional. First, we don’t worry about the loss of static charge because we can recharge later. The main purpose of washing surgical masks or N95 respirators isn't to eliminating bacteria, it’s to remove the dust blocking the airflow. The static charge does not only sticks to viruses, but also tiny dust particulars. Hot air treatment can kill bacteria but it cannot remove the dust. Human sweat and fats also block the air, similar to how acne forms on faces. After reading the material properties of melt-blown, water was the best affordable choice. It can dissolve mineral salts and soluble stains and wash away insoluble particulars when the static charge is gone. More than just soaking though, you need water to flow. So I used a small submergeable pump and a short piece of plastic hose. I put a piece of adhesive double-sided tape on the pump to affix it to the wall of the water tank. I also extended the wires to be about 50cm longer.

If you want a better wash, I suggest putting a heater inside. This helps kill bacteria and dissolve stains. It would be a great help in cold countries. Remember to add a sensor or a thermostat switch to control the water temperature.

Step 8: Other Accessories

You need two pieces of plastic net, listed in the material list, to hold the masks in place while they are being washed and blown. N95 respirators can be squashed to fit the net and without damaging them. You need some zip ties tied at one side to make a hinge so it can act as a net.

UVC exposure is harmful to humans so we need a door to block it. I came up with a simple solution. I cut a piece of PP hollow board that was 45 x 14cm. I drilled 4 holes, 4mm diameters each at 4 corners, and put 4 plastic rivets through them. The board can then be placed in between the gaps of the PC hollow board. Finally, I stick some velcro on two sides of the box and on the door to cover it. It looked rough but it worked. You can upgrade it with a hinge or reed switch with magnets to make it more secure like a microwave door.

I placed an OLED and 5 press buttons (four functions and one emergency reset) to the panel board. All buttons were soldered with XH2.54 2P wires. The OLED needed an XH2.54 4P doubles headed wire to connect.

Step 9: Control Boards

This prototype needed a lot of small upgrade to work better, so I left some plug-ins on the board. They were: door switch, a temperature sensor for the water tank, and two more analog inputs. Since there is a great possibility of errors caused by electrostatic charge - which also generates lots of ion in the air - there are a bunch of ESD protective parts on the board. Also, it takes 3 days for me to wait the board from PCB makers, a bit longer than estimated due to COVID-19 side effects.

I used LCEDA to draw the board. Pic2 shows the 3D renderring. Due to lack of some libraries of components, there are 2 blank spaces. One is 110V/220V AC to 5V DC power supply, located at top-right corner of the board. Another is LM2596 modules stacked in two. You can see what the board looks like in real in Pic 3.

Pic 4 is the AC-DC 110/220V to 12V switching power supply. There are three kinds of power in this device, AC power, DC 12V, and DC 5V. For stability reasons, I put another AC-DC 5V module specially for MCU, sensors, and relay controls. They were electrically isolated from the other actuators.

The high-voltage panel should be placed away from the other boards. When it is on, you will hear a mosquito-like buzzing sound. That's the electro-corona discharging. Pic 5 and Pic 6 are high-voltage panels.

The last picture shows every function connected to the board.

Step 10: Test Run

Let's take a look how to use the Box from Video 1.

I bought a PM2.5 meter, which was used by someone's home decoration before.
I've tested several times. The raw videos show the test result. The yellow digit is PM2.5 value.

Video 2: Old mask without cleaning and recharging

Video 3: PM2.5 test washed mask without recharging. It behaved worse than an old mask.

Video 4: PM2.5 test washed mask after recharging. It recovered the ability of blocking aerosols and tiny particles.

Step 11: Attachments

Here I share you the code and schematic. You need 123D Design to open the sketch or mock up file.

Step 12: Something Want to Tell

As pandemic still rages the world, we want to share and provide the kit to help people. We have launched a crowdfunding and want to figure out how many people need this.

In the campaign, there is another type of Mask Reborn Box. Here I show you Jason's work, Semi-PMRB PM0.3 test video.