How to choose the right filter media? Materials, Structure and Performance

Filtration is an omnipresent part of our daily lives. It is used in engine protection, industrial processes, air purification, water treatment, food production, etc. Its main role is to retain undesirable contaminants in order to protect equipment, guarantee the quality of finished products and ensure personal safety.
The nature of these contaminants varies greatly depending on the application: in hydraulics, we often encounter water, metal particles or residues linked to the degradation of fluids and wear and tear of moving parts in the circuit; in compressed air, they are more likely to be oil mists, dust and humidity; in water treatment, they are suspended matter or chemical substances. These are just a few examples: each process can generate or be exposed to specific contaminants.
These differences mean that a filter media must be chosen that is adapted to the fluid to be treated, the type of contaminants present and the conditions of use.

Whether surface or depth filtration is involved, the performance of a filter medium depends above all on its characteristics, which determine its compatibility with the intended application. To choose the most suitable solution, it is essential to examine these characteristics.

Some surfaces interact differently with water and oils: they may repel one but not the other, or they may repel both. These behaviours, whether natural or obtained by treatment, determine the adaptation of a filter medium to its environment.

• Hydrophilic / Hydrophobic: A hydrophilic medium easily attracts and retains water. This is the case with materials such as cellulose, whose chemical structure encourages moisture to adhere. Some media can also be modified by adding a super-absorbent polymer which, on contact with water, swells and turns into a gel, trapping the moisture. Conversely, a hydrophobic media repels water: droplets bead up and remain on the surface without penetrating. Polymers are naturally hydrophobic, but this behaviour can also be achieved by surface treatment applied to other materials.
• Oleophilic / Oleophobic: An oleophilic media attracts oils and hydrocarbons, which spread and impregnate its fibres easily. This is the case with polypropylene (PP), used for example in marine absorbents, because it repels water (hydrophobic) while effectively capturing oils. Conversely, oleophobic media repel oils: the droplets remain spherical and roll over the surface without impregnating it. This property is rare in nature, but exists in certain polymers such as PTFE (Teflon). It can also be obtained by specific surface treatments, used in particular to prevent clogging of filters exposed to greasy mists in the food industry or compressed air systems.

These surface properties are exploited in coalescing media, designed to separate two immiscible fluids such as water and oil, or air and oil mist. Their treated fibres encourage the adhesion of fine droplets that slide down the fibres, gather and grow until they form heavier droplets, which detach and fall by gravity.

Antistatic media limits the build-up of static electricity on its surface, reducing the risk of sparks and dust explosions. This property is achieved by incorporating conductive fibres (metallic or carbon) or by applying a conductive coating. These elements ensure that electrostatic charges are conducted to earth, where they are safely dissipated, preventing them from accumulating in the media.
This type of media is essential in sensitive environments classified as ATEX, where electrostatic energy must remain below the threshold that could trigger an explosion. They can be found in many sectors: wood, food processing, chemicals, pharmaceuticals and metallurgy. This property is also increasingly used in hydraulics.

A filtrant must withstand the chemical, thermal and mechanical stresses of the environment in which it is used.

• Chemical compatibility refers to the material's ability to withstand the fluid and its contaminants (water, acids, solvents, oils, etc.) without degrading or releasing undesirable substances.
• Thermal resistance refers to a medium's ability to retain its properties and structure under the effect of heat: some polymers remain stable up to 120°C, while metal alloys can exceed 500°C.
• Mechanical strength refers to resistance to pressure, load variations, abrasion, vibration and fatigue due to repeated cycles.

The joint assessment of these three parameters is essential to guarantee the filtability, performance and longevity of the filtration system.

Over time, the particles trapped by the media accumulate:

• Deep within the porous structure of the material, gradually reducing permeability.
• On the surface, where they form a filter cake, an additional layer retaining particles finer than those initially captured by the media.

This clogging, whether deep down or on the surface, increases the resistance to the passage of the fluid, which causes an increase in the differential pressure (ΔP) between upstream and downstream of the filter.
When the ΔP reaches the critical threshold defined by the manufacturer or by the process, the filter must be replaced or cleaned.
Some media can therefore be washed and regenerated, extending their life without compromising their performance, as long as they are cleaned properly.
Regular monitoring of the ΔP, combined with the use of maintenance indicators, is essential for planning replacement or maintenance, limiting unplanned shutdowns and maintaining filtration quality.

At HIFI FILTER®, we know that the performance of a filtration system depends on the choice of the right media, adapted to each application, environment and industrial constraint.
That's why we put our technical expertise, our wide range of solutions and our personalised support at the service of all sectors, even the most demanding.
Because a good filter is good. But a good partner is better.
Contact our experts for tailor-made support 👇