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What is a HEPA filter & how does it work?

You’ve probably heard the term ‘HEPA filter’ and may be aware that it refers to standards of filtration in devices like a home air purifier – but the specifics of how it works are probably less clear.

Sotiris Vardoulakis – Professor of Global Environmental Health at The Australian National University (ANU) National Centre for Epidemiology and Population Health, and a leading expert in air quality and pollution, underpins how HEPA can support health during flu season. “It is important to breathe clean air this winter season. HEPA filters can capture 99.95% of particles including bacteria and potentially some viruses. Evidence shows that appropriately used HEPA filters can improve air quality within a building”.

With the assistance of Ben Lowson – Engineer lead at Dyson, we’ve broken down common questions about the filter – including ‘what does HEPA stand for’ and ‘what does a HEPA filter do’.

To select the right home air purifier for your space, discover the features of Dyson’s HEPA air filter purifiers ahead.

HEPA filter in Dyson air purifier

What does HEPA stand for?

Meaning ‘High Efficiency Particulate Air’, HEPA refers to the quality and efficiency standards of filtrations. When a filter’s performance is certified as a HEPA filter, it means that it can capture 99.97% of particles down to 0.3 microns (tested by the IEST). ISO, another organisation defines a HEPA air filter as being able to capture 99.95% of MPPS particles (the most difficult to capture)..

The Dyson HEPA filter range of purifiers pass both of these tests. Included in particles of this size are allergens and dust mites, bacteria, particle pollutants and pollen, which all affect the health standards of homes. A home air purifier that doesn’t meet HEPA filter standards can be less effective at capturing and removing potentially harmful particulate matter from indoor spaces. By choosing a HEPA air purifier, allergens are less likely to trigger inhabitants and functions like sleeping are safer.

  • How does a HEPA filter work?


    A HEPA air filter is designed with intricate layers, in order to catch particles of microscopic size. Usually made from materials like PTFE or glass-fibre, each layer is arranged in randomly arranged sheets, which come together to form a kind of mat. Because particulate matter ranges in size, a HEPA filter traps in three different ways:


    • Larger particles: are trapped through impact, by hitting and sticking to a net-like formation of filter fibres.
    • Smaller particles: are intercepted as they move through air, becoming stuck on filter fibres.
    • Smooth particles: are the hardest to capture as they move through air flow randomly. The HEPA air filter is designed so that smooth particles collide with filter fibres as they move erratically with air.

  • Particles

Choosing a HEPA air purifier

Each Dyson home air purifier filter reaches the high HEPA standard. Other features range through each – the Dyson Purifier Cool Autoreact™ purifies the entire space1 against potentially harmful particles and provides a powerful stream to cool you down in warm weather. For added heating, the the Dyson Purifier Hot+Cool Autoreact™ also removes 99.95% of ultrafine particles2 and provides fast, even heated air for colder weather. Other HEPA filter considerations to make are below.

HEPA filter grade

Not every HEPA air filter is created equal. HEPA grades refer to their efficiency in capturing particles – a higher grade means higher efficiency. This is important for your home air purifier, as the best performance indicates filter efficacy alongside flow rate (filter ability versus the rate at which it filters). All Dyson purifiers achieve a H13 grade3 (in ISO standards), which is the ideal filter grade for removing particle pollutants while maintaining a powerful and consistent projection of air around the room.

Additional forms of filtration

Dyson HEPA air purifier designs don’t just rely on HEPA to protect and purify indoor spaces. Alongside the HEPA filter, additional forms of filtration include:


  • Activated carbon filter:
    Particles like bacteria and viruses aren’t the only pollutants that form in the home. Gas pollution such as N02 and VOCs (Volatile Organic Compounds) are created through home activities like cooking and cleaning, and also travel in through open windows and doors. Each Dyson home air purifier also contains an activated carbon filter – which effectively captures and absorbs many of the gas pollutants found in airflow.

  • Selective Catalytic Oxidation (SCO) filter:
    The Dyson Purifier Hot+Cool™ Formaldehyde features this third filter layer, which captures and destroys formaldehyde4. A gas-phase substance that can evade particle filters, formaldehydeoccurs through wood furniture and materials, carpets and paint. This substance can continuously ‘off-gas’, affecting the air quality in homes. An SCO filter uses the mineral Cryptomelane to destroy formaldehyde at a molecular level and convert it to CO2.

Winter tips for the cooler months ahead

Alongside HEPA filtration, other lifestyle habits can help protect you and your family during cooler seasons. Pair these tips with HEPA filter benefits for improved air quality for a cleaner, healthier home.

  1. Boost your immune system. Up your vitamin intake in winter, especially Vitamin C and eat a balanced diet providing your body with key nutrients to boost your immunity and help warn-off, or fight infection.
  2. Maintain your distance. Since the start of the pandemic, there has been a strong focus on social distancing. Continue to avoid mixing with crowds of people where possible, as well as anyone who you know is unwell such as friends or family members. In the same vein, ensure you isolate yourself from others if you come down with cold or flu-like symptoms to avoid spreading germs.
  3. Breathe clean air. We are all aware of the need for social distancing, cough and sneeze etiquette and the use of facemasks, but it’s also important to ensure good ventilation of indoor spaces. When appropriately used, HEPA filters for home with sealed HEPA 13 standard filtration can significantly improve indoor air quality. In Dyson’s latest HEPA filter air purifier, it’s not just the filter that meets HEPA H13 standard, but the whole machine. They capture 99.95% of particles as small as 0.1 microns5 including bacteria, mould spores, allergens and pollen. Using Dyson Air MultiplierTM technology, the machines can project purified air to every corner of the room and keep stagnant air that can cause mould, circulated.6
  4. Stay warm and dry. Rug up, stay hydrated and try swapping cold water for warm herbal tea.

Shop Dyson’s HEPA H13 air purifiers

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