If you’re shopping for an air purifier, you’re probably drowning in confusing terms. I see it all the time, and as a dad who’s spent years researching this, it drives me crazy. You see “HEPA-like,” “HEPA-style,” “99% HEPA,” and a dozen other phrases that sound official.
They are designed to be confusing.
So let’s cut right through the noise. Here is the single most important sentence you need to know:
The Quick Answer: A True HEPA filter is not a brand. It is a performance standard, defined by the U.S. Department of Energy (DOE), that requires a filter to be tested and certified to capture 99.97% of airborne particles at 0.3 micrometers (µm) in size.
That’s it. That’s the one, non-negotiable definition. Any product that meets this standard is a “True HEPA” filter, which stands for High-Efficiency Particulate Air. Anything that doesn’t is… something else.
Key Takeaways
- The “True HEPA” Standard: The U.S. DOE standard is 99.97% capture of 0.3-micron particles. This is the only number that matters.
- “HEPA-Like” is a Trick: Terms like “HEPA-like,” “HEPA-type,” or “HEPA-style” are unregulated marketing phrases with no guaranteed performance.
- The 0.3-Micron “Myth”: This is the hardest particle size to catch, not the smallest. HEPA filters are more efficient at capturing even smaller particles, including viruses.
- HEPA Does Not Stop Gases: A HEPA filter is for particulates (dust, smoke, pollen). It cannot remove odors, chemicals, or VOCs. For that, you need a separate Activated Carbon filter.
“True HEPA” vs. “HEPA-Like”: Spotting Deceptive Marketing
This is where most people get tripped up, and frankly, it’s what frustrates me the most. You’ll see an air purifier that’s half the price and labeled “HEPA-type” or “HEPA-style,” and you might assume it’s just a different brand or a slightly lower grade.
It is not.
These terms are unregulated. There is no legal or scientific definition for “HEPA-like.” It’s a marketing phrase used for filters that fail to meet the 99.97% at 0.3-microns standard. Some of these filters have been tested to capture as little as 55% of particles, making them vastly inferior.
This simple chart is all you need to know.
The “True” Standard vs. The “Empty” Terms
| Feature | True HEPA | “HEPA-Like” / “HEPA-Type” |
| The Standard | Captures 99.97% of particles at 0.3 microns. | No standard. Vague claims like “99% efficient.” |
| Authority | Defined by the U.S. Dept. of Energy (DOE). | None. An unregulated marketing term. |
| Verification | Can be independently tested and certified. | Not tested to any official standard. |
| Performance | Guaranteed minimum performance. | Unknown and unreliable. Can be as low as 55%. |
When you’re buying a product for your home’s health, you are buying this guaranteed performance.
How a HEPA Filter Actually Works (It’s Not a Sieve)
So how does it do it? Most people think a HEPA filter is just a microscopic window screen or a sieve that physically blocks particles smaller than its holes.
This is completely wrong. In fact, the spaces between the fibers in a HEPA filter are often much larger than the 0.3-micron particles it’s famous for catching.
The magic isn’t in blocking; it’s in capturing. The filter is a dense, random mat of fiberglass or synthetic fibers that creates a complex labyrinth for air to pass through. As particles try to navigate this maze, they are captured by three distinct physical mechanisms.
- Inertial Impaction (For Large Particles): Think of a big bug hitting your car’s windshield. Large, heavy particles (like dust, pollen, and mold spores) have too much inertia. They can’t follow the air’s curved path around a fiber, so they slam straight into it and get stuck.
- Interception (For Mid-Range Particles): This is for particles that are a bit smaller and can almost follow the airflow. As they flow past a fiber, they might “graze” the side and become snagged, like a fly grazing your car’s side-view mirror.
- Diffusion / Brownian Motion (For Tiny Particles): This is the most fascinating one, and it’s the secret to catching ultrafine particles. These particles (like viruses and smoke soot) are so small and light that they get battered around by individual air molecules. This makes them move in a wild, random “zig-zag” pattern. This random path makes it impossible for them to fly straight through the filter—they are guaranteed to eventually collide with a fiber and get trapped.
The MPPS: Why 0.3 Microns is the “Magic Number”
This brings us to the single most misunderstood part of HEPA filters: the 0.3-micron number.
Why that specific size? Because it’s not the smallest particle the filter can catch; it’s the hardest size to catch.
This is called the Most Penetrating Particle Size (MPPS).
Think about it:
- Particles larger than 0.3 microns are easily caught by Impaction and Interception.
- Particles smaller than 0.3 microns are easily caught by Diffusion.
But that “in-between” size right around 0.3 microns is the filter’s “worst-case scenario.” These particles are just small enough to avoid most impaction but just large enough to not be fully controlled by diffusion. They are the particles with the best chance of sneaking through.
The U.S. Department of Energy standard is brilliant. By forcing the filter to be tested against the hardest possible particle to capture, it provides a rock-solid guarantee. If a filter can catch 99.97% of its most difficult enemy, you can be confident it’s catching even more of everything else.
Myth-Busting: HEPA Filters, Viruses, and Nanoparticles
This leads us to the most dangerous myth I hear: “A virus is 0.1 microns, so a 0.3-micron HEPA filter can’t catch it.”
This is 100% false.
As we just learned, 0.3 microns is the minimum efficiency point (the MPPS). Because of Diffusion (Brownian Motion), the filter’s capture efficiency dramatically increases for particles smaller than 0.3 microns.
In fact, research from NASA and other independent labs has shown that HEPA filters are almost 100% efficient at capturing ultrafine particles down to 0.01 microns. Viruses, smoke, and other nanoparticles don’t stand a chance.
The Global HEPA Ecosystem: Understanding Other Ratings
When you shop, you’ll see other terms. Here’s what they mean.
European Standards: What Do H13 and H14 Mean?
In Europe, they use a slightly different standard (EN 1822 / ISO 29463) that classifies filters based on their efficiency at their specific MPPS. The two you’ll see are:
- HEPA H13: $\geq 99.95\%$ efficient at its MPPS.
- HEPA H14: $\geq 99.995\%$ efficient at its MPPS.
The U.S. “True HEPA” standard of 99.97% is roughly equivalent to the H13 classification.
What About MERV? (And Why It’s Not HEPA)
You might see a MERV rating on your furnace filter. This stands for Minimum Efficiency Reporting Value and is an ASHRAE standard for HVAC systems. It’s a scale from 1-16.
It’s simple: The MERV scale stops where HEPA begins. A MERV 16, the highest rating, is only required to capture $\geq 95\%$ of particles. True HEPA is a completely separate, much higher class of filtration.
What Is CADR? (Filter vs. System)
This one is critical. A perfect True HEPA filter is useless if it’s in a poorly designed machine that’s full of leaks.
CADR stands for Clean Air Delivery Rate. It’s a metric that measures the entire system’s performance—how much clean air the machine actually produces. It accounts for both the filter’s efficiency and the fan’s power. A high CADR means the unit can clean the air in your room quickly and effectively.
When you’re buying an air purifier, the “True HEPA” label tells you the filter is legit. The “CADR” rating tells you the machine is effective. This is a whole topic on its own, and you can learn more in our full guide explaining what CADR is and how to use it.
What HEPA Filters Can (and Cannot) Capture
Let’s put it all together. A True HEPA filter is a powerhouse, but it’s important to know its limitations.
✅ What HEPA Filters Are Designed For (Particulates)
- Dust
- Pollen
- Mold Spores
- Pet Dander
- Bacteria
- Viruses
- Smoke (Soot / Particulate Matter)
❌ What HEPA Filters CANNOT Capture (Gases, Odors, & VOCs)
This is the other critical mistake I see people make. A HEPA filter is a particulate filter. It’s a physical net, and gas molecules are simply too small to be caught by it.
It will not stop:
- Odors from cooking or pets
- Chemical fumes from paint or cleaning supplies
- Volatile Organic Compounds (VOCs)
- Smoke (The gaseous, smelly part)
To remove these, you need a separate filter technology, most commonly Activated Carbon. High-quality air purifiers will almost always include a substantial carbon filter alongside the True HEPA filter to tackle both particulates and gases. This combination is essential for specific problems. If you’re dealing with smoke from wildfires, you’ll want to see our recommendations for the best air purifiers for smoke.
What About a Pre-Filter?
You’ll often see “pre-filter” listed. This is a separate, upstream filter—often a simple mesh or foam—designed to catch large particles like pet hair, lint, and big dust bunnies before they reach the main HEPA filter. This is crucial as it extends the life of your expensive HEPA filter by stopping it from clogging up with big, easy-to-catch debris. Many of the units in our guide to the best air purifiers for allergies feature robust, washable pre-filters.
The Final Check: How to Ensure You’re Buying True HEPA
When you’re ready to buy, just follow this simple checklist.
- Look for the “Magic Words”: Ignore the hype. Look for the specific, verifiable claim: “Captures 99.97% of particles at 0.3 microns.” If a brand hides this number, be skeptical.
- Be Skeptical of Vague Claims: If it says “HEPA-like,” “HEPA-type,” or “99% HEPA,” it is not True HEPA.
- Check the CADR Rating: The HEPA filter is the engine, but the CADR rating tells you how fast the car goes. Make sure the unit is powerful enough for your room size.
- Look for a Carbon Filter: Unless you only have a dust problem, you’ll want a unit with an activated carbon filter for odors and gases.
When it comes to your family’s health, don’t settle for marketing tricks. The data is all that matters. “True HEPA” isn’t just a phrase—it’s a single, verifiable standard that guarantees performance. Anything else is just noise.
Frequently Asked Questions (FAQ)
What is the difference between a HEPA filter and a “True HEPA” filter?
“HEPA” is the name of the standard. “True HEPA” is a marketing term used by companies to communicate that their product actually meets that official standard (99.97% capture at 0.3 microns), as opposed to “HEPA-like” filters which do not.
What is the official government standard for a HEPA filter?
In the United States, the standard is set by the Department of Energy (DOE). It requires a filter to capture a minimum of 99.97% of airborne particles that are 0.3 micrometers (µm) in size.
Are “HEPA-like” or “HEPA-type” filters as good as True HEPA?
No. Not even close. These are unregulated marketing terms with no guarantee of performance. They are used for filters that fail the official DOE standard, and some may only be 50-60% efficient.
What particle size (in microns) do HEPA filters actually capture?
HEPA filters capture particles of all sizes with extremely high efficiency. They are tested at 0.3 microns not because it’s the smallest particle, but because it’s the most penetrating particle size (MPPS), or the hardest one to catch. Their efficiency is even higher for particles both larger and smaller than 0.3 microns.
What do the HEPA classifications (like H13 or H14) mean?
These are part of the European/International standard (EN 1822 / ISO 29463). H13 filters must capture $\geq 99.95\%$ of particles at their MPPS. H14 filters must capture $\geq 99.995\%$. The U.S. True HEPA standard is roughly equivalent to H13.
