Every air filter faces the same trade-off. Making a filter capture more particles usually makes it harder for air to pass through, which means higher energy consumption in ventilation systems or less comfortable breathing in masks. Electrospun nanofiber layers are studied because they can shift this trade-off in a favorable direction.

How fibrous filters capture particles

A fibrous filter is not a sieve. Particles much smaller than the pores are captured through several mechanisms working together:

  • Interception — a particle following the airflow passes close enough to a fiber to touch it.
  • Inertial impaction — larger particles cannot follow the air around a fiber and collide with it.
  • Diffusion — very small particles move randomly and eventually reach a fiber.
  • Electrostatic attraction — charged fibers or particles increase capture.

Thinner fibers are more effective at interception and diffusion, which is why nanofibers can achieve high efficiency with very little material.

Why pressure drop can stay low

When fiber diameter becomes comparable to the mean free path of air molecules, air “slips” past the fiber surface instead of sticking to it. This slip-flow effect reduces drag on each fiber. Combined with the low basis weight of a nanofiber layer, it allows high capture efficiency with a modest increase in pressure drop.

Comparing filters fairly: the quality factor

Efficiency or pressure drop alone can be misleading. Researchers therefore often report the quality factor:

QF = −ln(1 − η) / Δp

where η is filtration efficiency and Δp is pressure drop. A higher quality factor means better filtration for the same resistance. Comparisons are only meaningful when face velocity and test particle size are the same.

Test design matters

Many fibrous filters show the lowest efficiency for particles somewhere around 0.1–0.3 µm, the “most penetrating particle size”. Testing across a range of sizes gives a much clearer picture than a single number.

Typical research questions

  • How does fiber diameter affect efficiency and pressure drop?
  • What nanofiber basis weight gives the best quality factor on a given support?
  • How stable is performance under humidity and long-term loading?

Explore our air filtration research support to see how Fumalife works with filtration projects.