Air purifier filters: HEPA, electrostatic, electret, and disinfection
How filter types capture particles, what ions do, and how to interpret Daikin Streamer and Xiaomi disinfection claims.
Published
Sources checked on 11 October 2026. Brand features and laboratory claims apply to the specific products and conditions described.
An air purifier can capture particles, adsorb gases, and sometimes inactivate microorganisms. These are different functions. A filter that traps a bacterium has removed it from the passing air; that does not establish that it killed it. Likewise, a disinfecting feature does not establish how quickly the purifier clears particles from a room.
HEPA, washable electrostatic, and electret are useful terms, but they describe different things: filtration performance, a reusable collection system, and charged filter material. They are not three mutually exclusive grades.
Filter types at a glance
| Type | How it captures particles | Maintenance | What to check |
|---|---|---|---|
| HEPA | A high-efficiency fibrous filter; capture can include electrostatic assistance. | Follow the replacement schedule and cleaning restrictions for the specific filter. | Evidence for the HEPA claim, filter sealing, and whole-device performance. |
| Washable electrostatic collection cell | A powered system charges particles and collects them on plates. | Wash the approved cell as directed; let it dry before reinstalling. | Performance after use and cleaning, plus ozone emissions. |
| Passive washable electrostatic fabric | Static-prone layers attract particles without a powered ionizing section. | Wash and dry according to the filter instructions. | Actual filtration rating; “washable” alone says nothing about fine-particle efficiency. |
| Electret | Fibres retain an electrostatic charge that supplements mechanical capture. | Usually a replacement consumable; wash only if expressly permitted. | Efficiency over its service life and complete-purifier performance. |
The mechanisms above are described in the EPA technical summary, Air-Care’s washable filter explanation, and Honeywell Home’s electronic filter maintenance guidance.
HEPA: a performance claim
HEPA stands for high efficiency particulate air. The EPA’s HEPA explanation describes at least 99.97% capture at 0.3 µm. This is not a pore-size cutoff: smaller particles can also be captured, often more efficiently. A filter does not behave like a kitchen sieve that lets everything below a certain size through.
For a product claiming a particular HEPA class, look for the associated filter classification and testing method. A marketing label or a capture percentage at one particle size is not enough to establish every classification claim.
Filter efficiency also differs from whole-device CADR. Air has to reach the filter, pass through it rather than around it, and circulate through the room. Compare the complete machine at the fan setting you will use; the performance and noise comparison keeps those settings visible.
Washable electrostatic: two different systems
Powered collection cells
An electrostatic precipitator uses an electrical charging stage and collector plates. The reusable cell can reduce replacement purchases, but cleaning becomes part of maintaining performance. Honeywell Home, for example, specifies regular cleaning of its electronic cells and prefilters, while optional postfilters still need replacement. Its troubleshooting guidance calls for cells to be clean, dry, and correctly installed.
Check the exact manual before choosing a detergent or cleaning method. Permission to wash a collector cell does not mean the whole purifier, every filter layer, or another manufacturer’s cell can be washed in the same way.
Passive washable fabric filters
Some reusable HVAC filters also carry the “electrostatic” label. Air-Care describes static charge generated as air passes through its filter layers, with trapped particles released during washing. This differs from a powered collection cell. Manufacturer’s explanation.
Do not infer HEPA performance from either “electrostatic” or “washable.” Ask for a documented filtration rating and check that the filter suits the equipment. Reusability is a maintenance advantage, not a measurement of particle removal.
Electret: charged fibres
An electret filter combines fibrous capture with a retained electrostatic charge, without needing a powered particle-charging stage. Charge can improve capture while allowing relatively low airflow resistance, but its contribution can decline as the filter loads. EPA technical summary.
Electret and HEPA can overlap. Electret describes a mechanism; HEPA describes performance. Daikin’s Singapore range includes filters marketed as electrostatic HEPA, illustrating why the word “electrostatic” does not automatically mean washable plates. Daikin air purifier range.
Xiaomi describes the Smart Air Purifier Elite’s filter as melt-blown polypropylene fibres with electrostatic assistance. That is charged fibrous filtration; it is separate from the Elite’s powered plasma feature. Xiaomi Elite filter description.
Ions: collection and room deposition
Ionizers charge airborne particles. A device may collect them internally, or particles may settle onto walls, furniture, and other room surfaces. Settled material can later become airborne again. Removing a particle from the air this way does not establish microbial inactivation. The EPA’s ionizer explanation also notes that these systems do not themselves remove gases or odours.
Powered ionization can produce ozone, a lung irritant. Check model-specific emissions evidence and whether the ion function can be disabled. A passive electret filter is a different mechanism; its retained charge is not evidence that it emits ions or generates ozone. The EPA discusses ozone from electronic air cleaners in its ionizer guidance.
Daikin: Streamer and active plasma ions
Daikin Streamer is an internal plasma-discharge technology. Daikin describes high-speed electrons producing oxidative reactions that act on captured pollutants and adsorbed odours. In its purifier range, the company also describes treatment of internal filters and, on applicable humidifying models, humidifying components. These are manufacturer descriptions of the mechanism. Streamer explanation, Singapore purifier range.
Active plasma ions are a separate feature. Daikin describes them as acting outside the unit, while Streamer acts inside it. Feature availability depends on the model; do not treat every Daikin purifier as having both. Daikin’s air quality catalogue.
Daikin publishes laboratory evidence for Streamer, but its Singapore explanation explicitly distinguishes the testing apparatus from a finished purifier in a home. For example, the coronavirus experiments used a roughly 31 L acrylic box and quantified virus infectivity with the TCID50 method. Daikin cautions that actual product and room effects can differ. This supports a laboratory inactivation claim under specified conditions, not a guarantee of a sterile room or infection prevention. Daikin’s test descriptions and limitations.
Xiaomi: UV-C, plasma, and antibacterial coatings
Xiaomi’s disinfecting features vary by product and filter. The Smart Air Purifier Elite combines internal UV-C LEDs with a plasma generator releasing positive and negative ions.
Xiaomi reports 99.9% airborne influenza A (H1N1) removal in 30 minutes, citing Airmid Healthgroup report ASCR092598. The test used a 28.5 m³ space, maximum fan speed, and both plasma and UV enabled. This is a manufacturer-published account of external laboratory testing. The cited footnote does not specify the test standard. Because the complete purifier was running, the result does not isolate the added effect of UV or plasma from filtration. Elite features and test footnotes.
A different approach appears in the Smart Air Purifier 4 Compact Filter Pro: an antibacterial coating targeting bacteria adhering to the filter. Xiaomi cites laboratory coating results for E. coli and S. aureus, plus a separate anti-mould test. These are surface-treatment claims, not evidence that the same percentage of microbes is eliminated throughout a room. Filter Pro coating claims and test references.
Do not transfer an Elite UV-C claim to another Xiaomi model, or a coated replacement filter’s claim to an uncoated filter.
What to prioritize when comparing purifiers
For particle removal, start with whole-device CADR, noise at the intended setting, and maintenance costs. For gases and odours, look for separate evidence for sorbents such as activated carbon; a particle filter alone is not a gas filter. EPA technical summary.
For a disinfecting feature, ask what was tested: filter material, an internal surface, a separate apparatus, or the complete purifier. Look for the organism, exposure time, chamber size, fan speed, enabled features, and a comparison with the feature switched off. Without that comparison, a whole-device removal percentage cannot tell you how much the disinfecting add-on contributed.
Use the guide to performance and testing standards alongside the model comparison to keep filter claims, room-cleaning results, and disinfection evidence in context.