HEPA Filter

There are not different types of HEPA filters: a filter either conforms to the HEPA standard, or it doesn't. This includes filters marketed as "HEPA-Like", which may look like HEPA filters externally but do not perform to the required standard. There are, however, different grades of HEPA filters, which range from H10 through H14. The higher the grade, the higher the performance.
H10 to H12 filters are sometimes known as "True HEPA" filters. They trap less particles than the higher grade filters. H13 and H14 are known as "medical grade" HEPA filters. These filter 99.95% and 99.995% of all particles down to 0.3 microns, respectively.
Medical Grade HEPA is used extensively in industries that require extremely clean environments, such as medical manufacturing facilities and electronics manufacture, because they have such a high particulate retention rate.

HEPA filter media is often a non-woven fiber. Sometimes ceramic or synthetic in nature while often made from glass fiber, sheets of this non-woven fiber trap particles in four ways.

Impaction – As air flows through the filter media, larger particles (larger than about 0.5 microns) are heavy enough that while the air changes direction and flows around the fiber, the inertia of these heavier particles propels them forward, causing them to impact and stick to the filter media.
Diffusion – For the smallest particles (smaller than about 0.1 microns), they are so light they do not actually flow with air, instead diffuse through the air. Because they do not simply follow the air path around the filter fibers, they instead are most likely to impact the fiber and become trapped.
Interception – For particles not heavy enough to have inertia but not light enough to diffuse through the air stream, mid range particles follow the air stream as it goes around the filter fibers and are trapped when they touch the fiber as they pass by.
Sieving – This is what occurs when fibers are so closely spaced that particles simply cannot fit through the air space between fibers and become lodged. It works best with particles about 1 micron and larger.
The combined effect of all four methods of filtration demonstrate exceptionally high filtration of microparticles, with the weakest point being 0.3 microns. With a HEPA filter, even at this weakest point of filtration, the filter traps 99.97%.

HEPA filters are typically made of a dense mat of fine fibers. The most common material used for HEPA filters is fiberglass, which is formed into a pleated or folded structure to increase the surface area for capturing particles. The fibers in the filter are usually very thin, ranging from 0.5 to 2 micrometers in diameter.

In addition to fiberglass, other materials such as synthetic polymers, polypropylene, and polyethylene can also be used to make HEPA filters. These materials are chosen for their ability to effectively capture and retain particles of various sizes.

To enhance the filtration efficiency, HEPA filters may also have a coating of chemicals or substances that can attract and trap particles, such as activated carbon or charcoal. This helps to capture odors, gases, and volatile organic compounds (VOCs) in addition to solid particles.

It's important to note that not all filters labeled as "HEPA" meet the same standards. True HEPA filters must meet specific efficiency requirements set by regulatory agencies, such as capturing at least 99.97% of particles that are 0.3 micrometers in size. So, when purchasing HEPA filters, it's advisable to look for those that are certified and meet the appropriate standards.

What Is the Difference Between HEPA Filter Grades?
HEPA filters are classified into different grades based on their filtration efficiency. The most common HEPA filter grades are HEPA H10, H11, H12, H13, and H14. Here is a breakdown of the differences between these grades:

HEPA H10: This grade has a minimum filtration efficiency of 85% for particles as small as 0.3 micrometers. It is suitable for capturing larger particles such as dust, pollen, and pet dander.

HEPA H11: This grade has a minimum filtration efficiency of 95% for particles as small as 0.3 micrometers. It provides better filtration than H10 and is effective in capturing smaller particles, including mold spores and fine dust.

HEPA H12: This grade has a minimum filtration efficiency of 99.5% for particles as small as 0.3 micrometers. It offers higher filtration performance than H11 and is capable of capturing smaller particles, including some bacteria and viruses.

HEPA H13: This grade has a minimum filtration efficiency of 99.95% for particles as small as 0.3 micrometers. It provides even higher filtration performance than H12 and is effective in capturing smaller particles, including most bacteria and some viruses.

HEPA H14: This grade has a minimum filtration efficiency of 99.995% for particles as small as 0.3 micrometers. It offers the highest level of filtration among the standard HEPA grades and is capable of capturing the smallest particles, including most bacteria and viruses.

This is a benchmark for filter performance, but there is a certain amount of trust involved. Underwriters Laboratories (UL) has their own safety standard testing procedure for HEPA filter units. So an air purifier or filter manufacturer could get their filter tested by UL, and if it passes, the purifier can bear the UL mark (typically, the letters “UL” in a circle, sometimes with the specific safety or performance standard ID listed below it).

True HEPA: A consumer air filter labeled True HEPA should conform the closest to the DOE standard for a HEPA air filter. At its highest efficiency, it should remove 99.97 percent of all particles that are 0.3 microns in size. InvisiClean, Aviano, Medify, Airthereal, Honeywell, Winix, GermGuardian and Levoit all make air purifiers labeled as True HEPA. Eureka makes vacuum cleaner filters marketed as True HEPA as well.

HEPA Type: Calling a filter a HEPA Type filter is essentially meaningless, as it does not conform to any standard. It might be nearly as good as a HEPA filter, or it might be completely ineffective.

HEPA Like: This is a variation on HEPA Type, although it is less common. It is just a marketing term, and you should not assume any filter with this label conforms to the actual HEPA standard.

Permanent HEPA: These filters are marketed as meeting the HEPA rating, but are also able to be washed and reused rather than replaced. However, we do not recommend washing HEPA filters, even if they are intended to be reused, because the washing process likely causes small amounts of damage to the filter that reduce its effectiveness over time.

Absolute HEPA– This is sometimes used to mean the same thing as True HEPA, although sometimes it appears to indicate a claim of even better filtration power, up to 99.999 percent at 0.3 microns, according to Terra Universal, a company that makes filters for vacuum cleaners.