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We're basically used to wearing face coverings while out and about at this point, and you might have noticed that several masks have a small slot to place a filter for extra protection.

Adding a filter in between the layers of your face mask can help block airborne particles that might sneak through the fabric and can offer some much needed reassurance during these uncertain times.

Luckily, you don't have to spend a fortune on face mask filters, as there are several budget-friendly options available online. To help you get started, Shop TODAY consulted a few health experts to learn what filter materials are most effective, how often you should swap them out and where you can buy them online.

When used in conjunction with social distancing practices, cloth face masks can help slow the spread of coronavirus, especially with the delta variant spreading across the country. However, not all masks are created equally, and some offer more protection than others.

"Homemade masks use various cloth materials that are all much looser weave than a medical-grade mask, such as an N95, but those masks need to be reserved for hospital use and health care professionals who cannot maintain social distancing with patients under their care," said Dr. Ruth L. Bush, associate dean of medical education and a professor at the University of Houston College of Medicine.

Thicker, tightly woven materials offer more protection, and face masks should ideally have two cloth layers to make them more effective. If you're wearing a mask made of a thin fabric, adding another layer in the form of a filter can provide added protection.

"When placed in between the layers — such as with a pocket style opening allowing for insertion and removal — you could insert a filter which will make the mask more effective and provide extra protection against allowing viral particles into the air when you talk, cough or breathe," Bush said.

Medical-grade masks should be reserved for health care professionals who need them most, but that doesn't mean you can't add a little extra protection to your face mask.

Many brands have offered filters online throughout the last year. Experts also say household staples like coffee filters and paper towels can double as face mask filters in a pinch and should be inserted in between layers of fabric and replaced after each use.

"Many masks available for purchase online have a pocket or pouch in which you could add a filter. Masks that have a looser weave, are more porous or made of very thin fabric may protect others better with the addition of a filter," Bush said.

Of course, filters and face masks aren't the only way to protect yourself and others against coronavirus, but they sure can help. "Research has shown that some loosely woven masks only block 10-20% of particles, but by adding one or more layers of filter material, higher percentages of particles could be blocked," Bush said.

Tested to achieve 99.7% bacterial filtration efficiency (BFE), this filter is made with several layers — two outer polypropylene layers to block large particles, two inner nonwoven fabric layers to block smaller droplets and an enclosed layer of spunbond polypropylene to block droplets you exhale.

The term MERV stands for "Minimum Efficiency Reporting Value," and these filters block particles smaller than one micron in size.

"This type of filter is probably most useful for people who will be having sustained or frequent close contacts with other people, particularly people who are not themselves wearing any type of mask," Aronoff said.

"The higher the MERV value, the more efficient the filter will be in trapping airborne particles," Aronoff said. These lightweight filters are made of one of the highest MERV values around, and they fit comfortably in cotton face mask filter pouches.

This PM 2.5 activated carbon (also known as activated charcoal) filter blocks up to 95% of airborne particles — everything from germs and dust to chemicals and pollen — thanks to several strong layers, including a high-efficiency filter cloth and an anti-stick cloth. "A tighter filter can help prevent inhaling small droplets in the air we breathe," Aronoff said.

Five layers of fabric band together to create this PM 2.5 activated carbon filter. The material is effective at filtering chemicals and gasses and can serve as a nice face mask filter, as long as the mask is tightly woven.

Each Casetify mask comes with two filters to get you started, but the brand also sells a pack of 10 replacement filters formulated with five protective layers that block close to 95% of particles.

After testing these filters, global lab Nelson Labs found that they provide more than 95% BFE, which helps block harmful particles in the air.

"The virus spreads through respiratory droplets that another person breathes in or that land on a surface that is then touched and transferred to the person’s nose or mouth," Bush said.

As with any other filter, just make sure you test it with your mask and make sure air flows freely. "If your glasses are fogging up, then the material is not allowing air to flow through and your breath is going up, around the filter and out the sides of your mask," Bush said.

These activated carbon filter inserts are currently the No. 1 bestselling option on Amazon. With five layers of filtration, these breathable filters can also be used with face masks for outdoor activities.

While these inserts were specially made for Athleta's face masks, they also fit nicely inside other non-medical face masks.

These MERV13 filters can be trimmed to fit in both adult and kids' masks with filter pockets. The charge of the fabric is meant to attract particles and trap them to efficiently filter the air through the mask. According to the product description, these specific filters are also hydrophobic, so they won't absorb moisture over prolonged periods of time.

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This story was originally published on June 1, 2020.

Chrissy Callahan covers a range of topics for TODAY.com, including fashion, beauty, pop culture and food. In her free time, she enjoys traveling, watching bad reality TV and consuming copious amounts of cookie dough.