The resistance of the ultra-low resistance medium and high efficiency filtration unit (F7-F9 grades, resistance ≤ 60Pa@rated air volume) has a “non-absolute linear positive correlation” with the filtration efficiency – the core logic is: The improvement of filtration efficiency depends on the enhanced interception capacity of filter materials for particulate matter. However, the strengthening of interception capacity is inevitably accompanied by an increase in the resistance of air flow passage. But through technical design, the traditional shackles of “high resistance for high efficiency” can be broken, achieving a balance between “low resistance and high efficiency”. The following analysis is carried out from three aspects: principle, relationship characteristics, and technical optimization direction
I. Core Principle: The Intrinsic Relationship between Resistance and Filtration Efficiency
The resistance of the filter unit is essentially the energy loss when air flows through the filter material and structure. The filtration efficiency is the proportion of particles (≥0.5μm) intercepted by the filter material. The connection between the two stems from the “interception mechanism” of the filter material:
The implementation path of filtration efficiency
The filtration mechanism of high and medium-efficiency filter units mainly consists of “interception, inertial collision, and diffusion” (F7-F9 levels), supplemented by “electrostatic adsorption” through electrostatic charging. To enhance efficiency, the following methods should be adopted to strengthen interception:
Reduce the diameter of the filter material fibers (such as using sub-micron fibers) to narrow the gap through which particulate matter passes.
Increase the pleat density of the filter material (expand the effective filtration area) and prolong the contact time between the airflow and the filter material;
The film coating/electrostatic charging technology is adopted to enhance the adsorption capacity for fine particulate matter.
The core factors generating resistance:
The resistance mainly comes from “the air flow resistance of the filter material itself” and “structural resistance (frame, seal, air flow distribution)”, among which the resistance of the filter material accounts for more than 70%
The finer the filter material fibers and the lower the porosity, the greater the frictional resistance when the airflow passes through.
Excessively high fold density or uneven airflow distribution can lead to an increase in local wind speed and an exponential growth in resistance.
After particulate matter deposits on the surface of the filter material, it will clog the pores, causing the operating resistance to increase with the increase of dust holding capacity. However, the filtration efficiency will slightly improve in the initial stage (dust accumulation forms a “secondary filter layer”), but it will tend to stabilize in the later stage.
Ii. Relationship Characteristics: Non-absolute linear, with room for optimization
1. Fundamental rule: An increase in efficiency is inevitably accompanied by a rise in resistance (unavoidable).
Under the premise of the same filter material and the same structural design, there is a positive correlation between resistance and filtration efficiency
For example, the F7 grade (efficiency 85%-90%@0.5μm) filter unit of the same brand has an initial resistance of approximately 40-50Pa. After upgrading to F8 level (efficiency 90%-95%@0.5μm), the initial resistance will rise to 50-60Pa. If further raised to F9 level (efficiency 95%-99%@0.5μm), the initial resistance usually reaches 60-75Pa.
The core reason is that more efficient filter materials require a finer fiber structure or stronger electrostatic adsorption capacity. As a result, the frictional resistance and adsorption resistance when the airflow passes through will inevitably increase.
2. Key breakthrough: The technical design can break the strong binding of “high resistance for high efficiency”
The core value of the “Ultra-low Resistance High Efficiency” product lies in maintaining the efficiency of F7-F9 levels while keeping the resistance at ≤60Pa (far lower than the 70-100Pa of conventional high efficiency filtration units) through technological innovation. The optimization logic is as follows:

3. Changes in the relationship during the operation stage: Resistance increases, efficiency first rises and then stabilizes
The relationship between resistance and efficiency of the filter unit will change dynamically throughout its entire service life cycle:
Initial stage (0-3 months) : There is no obvious dust accumulation on the surface of the filter material, the resistance is stable at the initial resistance (40-60Pa), and the efficiency reaches the rated value (F7-F9 grade).
Mid-term (3-12 months) : Particulate matter gradually deposits, forming a “secondary filter layer”, with efficiency slightly increasing (about 1%-3%), and resistance slowly rising to 1.5 times the initial resistance (60-90Pa).
In the later stage (12-18 months) : The pores of the filter material gradually become clogged, and the resistance rapidly rises to twice the initial resistance (80-120Pa). The efficiency tends to stabilize (the secondary filter layer becomes saturated). At this point, the filter material needs to be replaced; otherwise, excessive resistance will cause a sharp increase in system energy consumption and even air flow short circuit.
Iii. Core Conclusions and Application Suggestions
The essential relationship: Resistance and filtration efficiency are in a “positively correlated but not strongly bound” relationship – efficiency improvement inevitably comes at the cost of resistance increase, but through filter material innovation, structural optimization, and technological empowerment (such as electrostatic charging), a “balance between high efficiency and low resistance” can be achieved, which is also the technical core of “ultra-low resistance, high medium efficiency” products.
Key points for product selection
Avoid the “efficients-only” approach: Some products, in pursuit of high efficiency (such as approaching F9 grade), overly reduce the fiber diameter or increase the wrinkle density, resulting in resistance exceeding 80Pa, which goes against the energy-saving original intention of “ultra-low resistance”.
Give priority to “gradient composite + electrostatic charging” products: such as the Bailun Purification ultra-low resistance high and medium efficiency filter unit, which adopts PP+PET gradient filter material + electrostatic charging technology, achieving a balance between F8 level efficiency (90%-95%@0.5μm) and initial resistance below 50Pa, taking into account both clean effect and energy-saving requirements.
System matching logic
If it is applied in scenarios with high air volume and 24-hour operation (such as data centers and electronic factories), it is necessary to prioritize ensuring “low resistance” to avoid excessive system energy consumption. Efficiency selection of F7-F8 grade can meet the requirements.
If it is applied in scenarios with high cleanliness requirements such as pharmaceutical D-level clean areas and food aseptic workshops, F8-F9 level efficiency can be selected. At the same time, the load can be reduced and the growth rate of operating resistance can be controlled by pre-filtering primary and medium-efficiency filters.
In conclusion, the core relationship between the resistance and filtration efficiency of ultra-low resistance medium and high efficiency filtration units is the “balance relationship after technical optimization” – on the basis of F7-F9 grade high-efficiency filtration, through the innovation of filter materials and structures, the resistance is reduced to the greatest extent, which not only meets the cleanliness requirements but also achieves energy conservation and consumption reduction. It is the preferred solution that takes into account “effect and cost”.