Surgical face masks are made with non-woven fabric, which has better bacteria filtration and air permeability while remaining less slippery than woven cloth. The material most commonly used to make them is polypropylene, either 20 or 25 grams per square meter (gsm) in density.

Surgical masks are made up of a multi-layered structure, generally by covering a layer of textile with non-woven bonded fabric on both sides. Non-wovens, which are cheaper to make and cleaner thanks to their disposable nature, are made with three or four layers. These disposable masks are often made with two filter layers effective at filtering out particles such as bacteria above 1 micron.

Masks are made on a machine line that assembles the nonwovens from bobbins, ultrasonically welds the layers together, and stamps the masks with nose strips, ear loops, and other pieces.

Respirators also consist of multiple layers. The outer layer on both sides is a protective nonwoven fabric between 20 and 50 g/m2 density to create a barrier both against the outside environment and, on the inside, against the wearer’s own exhalations. A pre-filtration layer follows which can be as dense as 250 g/m2. This is usually a needled nonwoven which is produced through hot calendaring, in which plastic fibers are thermally bonded by running them through high pressure heated rolls. This makes the pre-filtration layer thicker and stiffer to form the desired shape and keep it as the mask is used. The last layer is a high efficiency meltblown electret nonwoven material, which determines the filtration efficiency.

Spunbonding:
Spunbonding is a process by which fabrics are produced directly from a thermoplastic polymer such as polyester, nylon, polypropylene, or polyethylene.

The molten polymer is extruded through a spinneret, cooled slightly in the air, and laid on a moving conveyor belt to form a continuous web. As the web cools, the fibers bond.

Spunbond fabrics are produced by depositing extruded, spun filaments onto a collecting belt in a uniform random manner followed by bonding the fibers.

Our Spunbound process is continuously running so there is always a team of technicians keeping the quality consistent.
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Spunbonding

Quality Control

  1. Bacteria filtration efficiency in vitro (BFE). This test works by shooting an aerosol with staphylococcus aureus bacteria at the mask at 28.3 liters per minute. This ensures the mask can catch the percentage of bacteria it’s supposed to.
  2. Particle Filtration Efficiency. Also known as the latex particle challenge, this test involves spraying an aerosol of polystyrene microspheres to ensure the mask can filter the size of the particle it’s supposed to.
  3. Breathing resistance. To ensure the mask will hold its shape and have proper ventilation while the wearer breathes, breathing resistance is tested by shooting a flow of air at it, then measuring the difference in air pressure on both sides of the mask.
  4. Splash resistance. In splash resistance tests, surgical masks are splashed with simulated blood using forces similar to human blood pressure to ensure the liquid cannot penetrate and contaminate the wearer.
  5. Flammability. Since several elements of an operating room can easily cause fire, surgical masks are tested for flammability by being set on fire to measure how slowly it catches and how long the material takes to burn. ASTM levels 1, 2, and 3 are all required to be Class 1 flame resistant.

Filtering facepiece respirators (FFR), which are sometimes called disposable respirators, are subject to various regulatory standards around the world.


Respirators certified as meeting these standards can be expected to function very similarly to one another, based on the performance requirements stated in the standards and confirmed during conformity testing. One notable comparison point is the flow rates specified by these standards for the inhalation and exhalation resistance tests. Inhalation resistance testing flow rates range from 40 to 160L/min. Exhalation resistance testing flow rates range from 30 to 95 L/min.

Based on this comparison, it is reasonable to consider China KN95, as “equivalent” to US NIOSH N95 and European FFP2 respirators, for filtering non-oil-based particles such as those resulting from wildfires, PM 2.5 air pollution, volcanic eruptions, or bioaerosols (e.g. viruses).

PPE HERO
PPE HERO