MAHLE cabin air filters—designed for fresh air

Cabin air filters are very efficient: During only one hour of driving, an air volume of up to 100,000 liters is circulated through the vehicle interior. All the more reason to change cabin air filter elements regularly. MAHLE recommends changing the cabin air filter every 15,000 km or a minimum of at least once per year. If the cabin air filter fails or is clogged, the pollutant concentration in the interior of the vehicle can increase to six times of that of the outside air. MAHLE cabin air filters reliably supply the driver and passengers with clean air to breathe, which safeguards their health, well-being and ability of the driver to concentrate even in the event of smog or high pollen count. They also reduce the load on the blower, protect heating and air conditioning from contamination, improve air circulation and prevent dangerous fogging of the windows. In addition, the inside of the windows and fittings remain cleaner for longer.

The pleat geometry of our cabin air filter elements is designed to provide a long service life. The low flow resistance minimizes the load on the blowers. Thanks to the accurate fit of the filter elements in the housings, bypass air is prevented.

Our cabin air filters produce no harmful emissions, as solvent-free methods, such as ultrasound welding technology, are used for their production.

Cabin air filters with activated carbon elements remove harmful exhaust fumes, dirt and dust as well as high ozone concentrations and unpleasant smells. Their pleat bellows consist of three layers: an activated carbon layer is sandwiched between two layers of non-woven materials. A heat process is used to fuse the filter layers and therefore no solvent containing glues are required. Depending on the vehicle type, activated carbon filters are also available that can be used instead of conventional cabin air filters.

MAHLE cabin air filters

Vehicles that were not originally equipped with cabin air filters can be retrofitted with our cabin air filters, including those with activated carbon. For that purpose, a filter element from our comprehensive program is matched to a housing that is suitable for the particular vehicle.


Car manufacturers have been using cabin air filters for many years now to make sure that the passengers get enough clean air to breathe. Whether passenger cars, trucks, buses or agricultural and construction machinery: almost every vehicle today has a “cleaner”—either as a simple particulate filter or combination filter with activated carbon layer. Particulate filters filter solids out of the air we breathe and protect us against fine particulate, pollen, industrial dusts and other microscopic, respirable particles. Activated carbon filters also absorb smells and toxic gases such as nitrogen oxides, petrol vapours or fertilizers and break down up to 99 % of ozone.

Additional coarse filters are often used in vehicles with a long service life that are operated in heavily polluted areas. This type of filter mat can often be seen in traffic as roof-top structures on buses. Others are fitted in the air intake system before the actual cabin air filter and installed as pre-filters in the heater and air-conditioning casing. These coarse filters are used to ensure the maximum filter service life for the complete filter surface area of the cabin air filter: if a mass of coarse particles hits the fanfold surface of the filter this can lead to a premature clogging of the inlet side of the air filter—even to the dreaded pleat bellows clogging that prevents the passage of any air at all. Upstream coarse filters can reduce one-sided clogging of the surface of the cabin air filter on the inlet side, thus helping to ensure that the entire filter capacity is used before the cabin air filter is changed during routine inspections.

Pre-filters are normally made of polyester foams or fleece mats. The choice of material depends on the specifications of the vehicle manufacturer.

Polyester foams consist of a homogeneous block with uniform pores produced by a special thermophysical process, reticulation. After cooling the foam is cut into slices and shaped by cutting dies.

Reticulation – what’s that?
Reticulation is the term used to describe the subsequent removal of foam membranes in a pressure vessel charged with gas. This process produces a uniform, open pore lattice structure with a minimum flow resistance for gases and fluids.

The filter effect of the reticulated material depends on the pore size PPI (pores per inch, in other words the number of open linear pores per inch = 25.4 mm). The higher the PPI number the smaller the particles that can be filtered. Common foams have between PPI 10 and PPI 80. MAHLE Original and Knecht LAP pre-filters are made using foams with a PPI of 30 since extensive laboratory tests have proven the optimum relationship between service life and coarse particle filtration for this pore size.

Polyester foam is resistant to ozone and partly resistant to hydrolysis, it withstands ageing and temperatures up to 90 °C and it is free from plasticizers and CFCs. The material can be recycled and poses no problems for thermal disposal.

These fleece mats are based on approx. 10 and 20 mm thick polyester fibre mats that are made up of various, progressive layers so that they become denser and denser on the clean air side. This structure combines a maximum filter performance with optimum dust retention properties.

Filter mats are classified in filter classes according to DIN EN 779.

Filter classFiltration efficiency
G2up to 80 %
G3up to 90 %
G4> 90 %

Weights of between 100 g/m² and 200 g/m² are used depending on the requirements. For example, a G2 filter mat with a weight of 100 g/m² will primarily stop coarse particles whereas a G3 filter mat of the same thickness and a weight of 200 g/m² can filter out much finer particles.

Polyester fleece is hardly flammable (classification of inflammability F1), resistant to hydrolysis, withstands ageing and temperatures up to 100 °C. The material is free from silicon, plasticizers and CFCs, can be recycled and is suitable for thermal disposal.

The surface of the cabin air filter can become clogged with coarse dirt particles—right through to pleat bellows clogging (see left)—whereas the lower depths of the pleats remain relatively clean (see right). A pre-filter protects against this premature wear (LAP).

Since the coarse filters are often located in front of the actual cabin air filters they can usually be replaced with no great effort by the driver. Only a few steps are needed and these are described in detail in the MAHLE fitting instructions (see illustration example).

LAP filters are either used as pre-filters in addition to particulate filters (LA) or as combi-filters (LAK). Older commercial vehicles only filter the outside air for the driver’s cab through filter mats. MAHLE Original and Knecht cabin air filter mats (LAP) are also available for a number of these commercial vehicles.

MAHLE is one of the top suppliers of cabin air filter mats on the free aftermarket. Following a successful market launch the range of products is constantly expanded, with a focus on commercial vehicle applications and older passenger cars as of model year 1980. Popular examples include the Renault Truck Midlum or Volvo 760. Cabin air filter mats will also be available as of October 2010 for commercial vehicles from DAF, MAN, Mercedes, Neoplan, Saab, Webasto or cars such as the Mercedes-Benz S-Class.

During only one hour driving, an air volume of up to 100,000 litres is blown into the vehicle interior. All the more important is the regular replacement of the cabin air filters. The MAHLE filter experts recommend: replace filters after every 15,000 km or at least once per year. If the cabin air filter is clogged up or fails completely, the pollutant concentration in the interior of the vehicle can increase up to six times of that of the outside air. MAHLE cabin air filters supply driver and passengers reliably with cleaned air to breathe and safeguard their health, well-being and the driver’s ability to concentrate even in the presence of smog or high pollen count.

Dirt particles such as dust, pollen or soot, harmful exhaust fumes, high ozone concentrations, unpleasant odours and even fine particulate dust: all these are retained by the cabin air filter – provided it is a combi-filter (LAK) that consists of two fleece layers and an active carbon layer, like this one. Due to the sandwich construction of the combi-filter (see also the scanning electron microscope image), two independent functions have been combined in one filter. The gases (mainly hydrocarbons as well as inorganic and harmful gases such as hydrogen sulphide, sulphur dioxide and nitrogen oxides) are here absorbed by the active carbon layer.

Sandwich construction under the scanning electron microscope: combi-filter (LAK), consisting of two fleece layers with an active carbon layer between them.

A saturated filter reduces the blower output and therefore delays significantly clearing of steamed up windows. If the filter change is postponed for too long, moisture binds to the accumulated dust: the filter becomes a breeding ground for bacteria and mould, which settle in the ducts of the ventilation and air conditioning system and lead to extremely unpleasant odours and harmful emissions into the vehicle interior. We like to give you therefore some tips for fast and safe filter change.

Spring, summer, autumn and winter: the cabin air filter during the course of the year:

Spring may be the main time for changing cabin air filters, but a look at the filter fleece shows: there is always plenty to collect.





In spring, for instance, one can recognise pollen, grass seed and relatively coarse dirt particles. These can even lead to clogging on the surface of the pleat bellows – while the pleats further down remain comparatively clean.

In summer, significantly more soot and fine dust can be found in the filter.

In autumn, the situation is similar to that of summer – however, due to the high air humidity, even more dust and other particles are collected more quickly.

Winter: the year reaches its end and so does the air filter. The filter is so dirty that it can no longer fulfil its intended purpose and will have to be replaced.

Depending on the vehicle type, the cabin air filters are located in different areas. To avoid searching for the fitting location, we recommend a look at the CD-ROM “Filter product range” or straight inside the packaging for the MAHLE Filter and Knecht cabin air filters. This is where you can find the printed fitting instructions – clear and always available, saving time and money in the workshop. For easy access, a tear-open strip is integrated in the packaging.

One of the most frequent fitting errors is placing the filter the wrong way round. The correct fitting orientation is exactly described in the vehicle specific instructions. In addition, the flow direction of the filter is indicated with small arrows at the side strip. Also the correct positioning of recesses and fixing projections should be observed.

In order to assure correct fitting of the cabin air filter, several things need to be observed during fitting. The MAHLE filter experts have chosen the LA 71 or LAK 71 as graphic example. These cabin air filters are supplied by MAHLE as original equipment and are fitted, for instant, in the DAF CF85 and XF95 from model 01/01 or 09/02 onward.

The frame of the LA 71 behind the front panel of the DAF CF85/XF95. The flow direction should be observed during fitting (see arrows, which point here in direction vehicle).

At first, the filter is slid under the two plastic retainers, while the two grip strips (1) point here downwards.

The filter is then carefully pushed into the frame until the plastic tab clicks into the intended recess. Care should here be taken to avoid damage to the plastic foam seal.

This is the correct position of the filter: the plastic tabs are engaged correctly, the frame seals perfectly and keeps out particles including fine particulate dust.

An obvious fitting error: the plastic tab is not at the intended position (1). The result: the frame bends sharply and the pleats deform (2). This bends also the foam seal – and a gap is formed, allowing dirt to enter freely the interior (arrow).

The commercial vehicle market is booming. This will also enhance the sales prospects for cabin air filters in lorries, transporters and building vehicles. Air conditioning systems with suitable filters have become all but standard equipment in the meantime. However, when a vehicle is used with a clogged cabin air filter, severe consequences for heating and air conditioning systems may be the result. The replacement intervals stipulated by the vehicle manufacturers must therefore be strictly observed. Generally this means: about every 12,000 to 15,000 km. For a lorry that travels an annual distance of 250,000, this would be at least every 3 weeks.

While some years ago only passenger cars were equipped with cabin air filters, there is practically no commercial vehicle today that is not fitted with a filter that protects drivers from polluted air entering the cabin. And that is a good development. Without cabin air filters, drivers in their cabins would be subjected to pollutant concentrations 6 times higher than at the roadside. This is mainly due to the so-called tunnel effect, which means that the exhaust fumes of the vehicles in front are directly drawn into the vehicle interior. But also irritant gases such as ozone, toxic gases such as fertilizers and diesel exhaust particulate and other irritants such as pollen and annoying smells would get straight into the interior without cabin air filters. MAHLE Filter and Knecht cabin air filters are both available as particulate and combination filters. Particulate filters protect from fine dust, but also from pollen, industrial fallout and other very fine particulates that can reach the lungs. In addition, active carbon filters absorb smells and gases and reduce up to 99 % of ozone.

A layer of special active carbon granules is sandwiched between two fleece layers. The unpleasant smells are deposited in the pores of the active carbon. Active carbon consists mainly of carbon (mostly > 90 %) with an extremely porous structure. The pores are interconnected like in a sponge. Just 2 grams of active carbon are roughly equivalent to the surface area of a football pitch – a standard filter containing about 200 g carbon has therefore a filter surface of about 100 football pitches.

In contrast to passenger vehicles, commercial vehicles are often used in dusty environments such as building sites. Their cabin air filters must therefore not only eliminate smallest particulate from the cabin, but also coarse particulate. However, the finer the filtration, the more dirt is removed – and the faster the dirt absorption capacity is exhausted. It is the task of the R&D engineers to combine the required fine filtration with a long service life. When the coarse particulate load is extremely high as, for instance, at a building site or a quarry, the filter must be replaced more often – or there needs to be a way of cleaning it. During the development of the LA 43, the decision was made in favour of cleaning.

The fleece of the LA 43 is supported and protected by a grid on both sides.

The higher the degree of air pollution, the sooner the filter will clog. In extremely dusty environments, the cabin air filter can become so dirty in a few hours that the ventilation system practically ceases working. For such extreme situation, MAHLE has developed the filter element LA 43 in cooperation with Mercedes- Benz. The filter can be cleaned by knocking out the dirt manually and is used as original equipment in the building site versions of the Actros and Actros II models.

The design of the filter has been modified to make it resilient to the cleaning process that is required several times daily under extreme dust loads. From the outside, the special filter differs from other MAHLE cabin air filters in its more robust construction, with stable aluminium side members and massive end-mouldings made from plastic. Optimum sealing is achieved with a so-called blade location in the end pleat of the fleece and a plastic foam seal all around. A corrosion-resistant wire grid at both sides supports and protects the filter fleece. The filter medium consists of a synthetic filter fleece that has been designed for a significantly higher dust take-up capacity for this application.

The LA 43: robust design with side members of plastic (1) and aluminium (2) as well as a foam seal all around (3).

Cabin air filters are mostly located in front of the vehicle's heating or air conditioning system, where the polluted outside air is drawn in and blown into the vehicle interior after cleaning – this can be up to 150 l air per second when the filter is in optimum condition. For clogged filters, this air volume is reduced. This can be noted clearly, when only a limited amount of air reaches the passenger compartment, although the blower is set to maximum (if in doubt, a visual check of the filter will help). When the filter is clogged, it is high time for replacement, or in case of the LA 43 for cleaning – regardless of the distance covered since the last filter change. If this is not done, expensive consequential damage of heating or air conditioning can result.

The cleaning process for the LA 43 can be repeated up to 80 times. Tests in laboratory and practice have shown that even after 80 cleaning procedures (tapping out and blowing out) the initial conditions of a new filter are almost reached again. However afterwards, the filter should be replaced as the performance can deteriorate rapidly.

Pre-cleaning: tapping the filter on an even surface releases most of the dirt located at the dirty side.

Also for the LA 43, the fitting orientation must be observed the same way as for any other filter.

Main cleaning: If compressed air is available, the filter can be blown out afterwards. However, this should only be done from the clean side, which means in opposite direction to the arrows at the outer moulding (see picture). Otherwise, the dust particles are blown through the material and the collection efficiency, especially for smaller particles, is significantly reduced, making the filter useless. Also the choice of air pressure is important: to maintain the long service life of the filter and to avoid damage, the air pressure generally used in workshops should not be applied. Less is better here, in particular in respect of service life. This means: do not hold the air nozzle too close to the filter, but keep a distance of about 10 to 15 cm and blow out the filter with low air pressure (max. 0.5 bar).

If there is no compressed air available, it is quite sufficient to tap the dust out of the filter and at the next opportunity clean it with compressed air as described above. When the filter is installed again, observe the correct fitting orientation – as indicated by the arrows at the side mouldings.

Note: although the cleanable filter is robustly constructed, it should be checked for possible damage before refitting and be changed when in doubt.