【Performance Comparison】Explaining the features of nanofiber face masks

Currently, nanofiber masks are beginning to be widely used in the medical field as “the highest standard fae masks” in contrast to conventional face masks! This article introduces nanofiber face masks along with our “MIKOTO” product.

A face mask with proven filtering performance at the world’s highest standard

The need to prevent “droplet infection” and “infiltration of blood and body fluids” in the medical field demands high-performance face masks, and therefore, standards for judging their performance are necessary.

The performance of most of the face mask products distributed in Japan is judged based on the standards set by ASTM International (International Standardization and Specification Organization) in the U.S. Our product, “MIKOTO” has passed Level 3, the highest standard of ASTM International.

U.S. medical mask standard (ASTM F2100-19)

characteristic Level 1 Level 2 Level 3 「MIKOTO」
Bacterial filtration rate (%) ≧95 ≧98 ≧98 99.9
Particle filtration rate (%) ≧95 ≧98 ≧98 98.5
Exhalation resistance (mmH2O/cm2) <5.0 <6.0 <6.0 4.0
Blood impermeability (mmHg) 80 120 160 160
Fire resistance Class1 Class1 Class1 Class1

The properties of Mikoto

Our Mikoto face Mask, is 100% made in Japan and offers unparalleled high performances.


  • Capable of catching up to 99% of virus-sized particles
  • Performance does not deteriorate even after washing
  • After opening the package, the mask always maintains its performance as long as the mask itself is not damaged.
  • Fits perfectly thanks to its three-dimensional shape
  • High breathability

The following is a specific explanation of these performances.

How Mikoto is different

The following is an comparison of the performance of MIKOTO with the performances of N95 face masks, face masks for particulates that meet and are approved by the United States National Institute for Occupational Safety and Health (NIOSH) N95 standard.

Particle Filtration Principle of Nanofibers

“Van der Waals forces” and “large surface area” are the reasons why nanofibers have both high filtration performance and durability.

The Van der Waals forces

The force of attraction between molecules is called “Van der Waals force”. In the case of MIKOTO, it is the force that attracts and holds microscopic particles such as viruses to the mask fibers themselves.

Surface area of nanofibers

Viruses are attracted to mask fibers by van der Waals forces. The greater the surface area of the fiber, the more viruses can be adsorbed.

Let’s compare the surface area of Mikoto with the one of “N95 face masks”

N95 Face Masks Medical Nonwoven Masks 「MIKOTO」
Fiber diameter 1〜3μm 1〜3μm 0.08〜0.4μm
Surface area ratio 1 time 1 time 300 times

If the N95 face mask filter can catch 100,000 viruses, MIKOTO can catch 30 million viruses, which is 300 times more than N95!

Most importantly, the filtration performance is not affected by washing the mask. As long as the nanofibers maintain their unique shape, the filtration performance will not deteriorate.

About filter performances

Filter performance tests for face masks include the following types

Types of face masks performance tests

PFE 0.1μm microparticles filtration efficiency test → test to determine if 0.1μm particles can be blocked
BFE Bacteria droplet filtration efficiency test → test to determine if bacteria can be blocked
VFE Virus droplet filtration efficiency test → test the ability to block viruses

Since viruses are as small as 0.1μm, a PFE or VFE of 99% or higher means that the filter is capable of blocking more than 99% of viruses.

And since the N95 face masks have their own standard of “blocking 95% or more of microparticles 0.3 μm or larger in size”, these tests are not required to be certified as N95 mask filters.

The table below compares the results of each performance test MIKOTO underwent compared to the N95 face masks.

PFE Over 98% No standards
0.3μm particles 95% or more ( in-house research) Over 95%
BFE 99.9% No standards
VFE 99.8% No standards

As a result, MIKOTO

  •  Achieved N95 mask filter standard of blocking 95% or more of 0.3-μm particles
  • Blocks 98% or more of virus-equivalent particles
  • Blocks 99.9% of bacteria
  • Blocks 99.8% of viruses

As proven by the tests

Easy breathing

The index of a face mask’s breathability is called “pressure drop,” and the lower the number, the more breathable the face face mask is. The following table compares the pressure drop across MIKOTO and N95.

Pressure drop 39.2 pascal 343 Pascal or less

The N95 face mask filter only allows air to flow vertically, and after about 30 minutes of wearing it, the user will feel difficulty in breathing. However, nanofiber masks allow air to flow horizontally, where air resistance is lower, so more air can be taken in compared to N95 face mask filters, and filtration efficiency is also improved as more air hits the fibers. This is called the “slip-flow effect”. This slip-flow effect makes it easier to breathe while using MIKOTO!


MIKOTO is a nanofiber face mask that has achieved ASTM Level 3 compliance, which is a high level of performance even when compared to global standards. We will continue to promote the use of MIKOTO so that it can be used by people in various industries, including those in the front-line medical field, those in the hospitality industry who are in close contact with others, and those in the nursing care industry.