From polypropylene to nonwoven fabric to face masks, do you really understand these basics?

Masks are made of nonwoven fabric, which, unlike woven fabrics, consists of oriented or randomly arranged fibers.

Medical masks typically have a multilayer structure, commonly referred to as the SMS configuration (two S layers and one M layer). At present, the highest-layer configuration in China is five layers, designated as SMMMS (two S layers and three M layers).

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Here, the “S” stands for the spunbond layer, whose fibers are relatively thick, with a diameter of about 20 micrometers (μm). The most critical component of the mask is the barrier layer, or the meltblown layer, designated as “M.” The meltblown layer features much finer fibers, approximately 2 micrometers (μm) in diameter—just one-tenth the thickness of the spunbond layer. This makes it highly effective at blocking bacteria and blood penetration.

Image source: Public information

Typical medical masks usually use 20 grams of meltblown fabric, while N95 cup‑style masks employ meltblown fabric weighing 40 grams or more.

According to statistics from the China Industrial Textiles Industry Association, as of the end of 2018, the country had 1,477 spunbond production lines, an increase of 65 compared with the previous year, or 4.6% year on year. Among these, PP spunbond nonwoven fabric lines grew by 3.38%, SMS composite lines expanded by nearly 13%, and PET spunbond nonwoven fabric lines increased by 9.32%. The number of enterprises with annual output exceeding 50,000 tons also rose compared with 2017. Spunbond producers are accelerating their transition toward larger scale, greater intensification, and higher-end operations, thereby more swiftly meeting market demand for product and technological upgrades.

Since 2018, numerous domestic companies have been developing products that are lighter, thinner, and higher-performing, achieving promising results. The SSMMS spunbond–meltblown composite process operates smoothly at high speeds exceeding 600 m/min, yielding ultra‑soft, lightweight, and stable nonwovens with a basis weight of approximately 10 g/m².

Where does SMS nonwoven fabric come from?

SMS nonwoven fabric uses polypropylene (PP)—which possesses natural antibacterial and hydrophobic properties—as its primary raw material, with fiber diameters ranging from 0.5 to 10 microns. These ultrafine fibers, characterized by a unique capillary structure, increase both the fiber density and the surface area per unit area, giving meltblown fabric excellent air filtration performance and making it a relatively superior material for face masks.

Currently, the main manufacturing processes for SMS products (SMS nonwovens) comprise three methods: the “one-step method,” the “two-step method,” and the “one-and-a-half-step method.”

The one-step process is characterized by using raw‑material chips and employing both spunbond and meltblown techniques to directly melt and spin the material into a fibrous web. By appropriately configuring the spinning systems for each process, products can be tailored to different structures; after laminating and bonding the individual fiber layers, the composite is typically consolidated into a nonwoven fabric using a thermal calender. A key feature of the “one-step method” is that it spins the molten polymer directly into a web, with independent control over each spinning system, resulting in highly controllable production, excellent hygienic conditions, and rapid processing. Moreover, the proportion of each layer in the web can be freely adjusted, enabling the manufacture of SMS‑type products in a wide range of specifications—making this approach the mainstream technology today.

Two‑step method: When producing SMS products using the two‑step process, the finished spunbond fabric and the finished meltblown fabric are laid out in a specific sequence, laminated layer by layer, and then consolidated with a hot‑roll calender to form the SMS product. The two‑step method is characterized by its simple equipment and low cost. In practice, this “two‑step” process is a widely used lamination‑based composite technique. It can also be employed to laminate other materials, utilizing various bonding methods—such as ultrasonic sealing or hot‑melt adhesive—to bond the three layers together.

One-and-a-half-step method: In the two-step process, the meltblown web produced on-site can also be used to replace conventional meltblown fabric, giving rise to the so‑called “one-and-a-half-step” composite technology. A spunbond fabric is fed through two unwinding units to form the base and top layers, while the intermediate meltblown web is directly spun into a fibrous web by the meltblown system and laid onto the surface of the base spunbond layer; this is then covered with the top spunbond layer. The resulting laminated structure is typically consolidated into an SMS product using a thermal calender.