What materials are medium filters made from?

Introduction

Media format also varies. Pleated panels, bag pockets, V-bank packs, and roll media are all in common use, so no single construction should be treated as the default when the question is what are medium filters made of. This article focuses on the subject of medium efficiency filters per se.

HEPA (high-efficiency particulate air) filters and ULPA (ultra-low penetrating air) filters are not medium filters because their cleanroom air filter materials are ultra-fine glass fiber paper, thermoplastic spacers, and anodized or plastic frames. They appear here only as contrast, so buyers do not mistake terminal filter materials for medium filter materials.

This article will define medium efficiency filters, examine the medium air filter media chemistry used in these particular filters, show how the medium is selected based on performance data, and review HVAC medium filter construction, operating limits, standards, and a project-reported case.

Technical review of this article was performed by Jason Peng, product designer, Deiiang, who verified application data and manufacturer's catalog values quoted in this document. Catalog data is labeled as manufacturer-published specifications throughout and is not presented as independent test results.

What Counts as a Medium Filter?

A medium filter may be referred to as a particulate air filter that falls between coarse prefiltration and high efficiency filtration. It is designed for use over a wide particle size range and not a specific size. In building services, medium-efficiency HVAC filters are used in air handling units and function as pre-filters to HEPA filters.

The distinction between a medium filter and a HEPA filter lies in the classification, not in the appearance of the media. For instance, a pleated pack of fine glass fiber paper tested using EN 1822 is a HEPA or ULPA filter regardless of how similar it is to a pleated medium filter in an image.

The drawing depicts a medium filter with its frame, pleated media pack, supports, and gasket. Please note that this is a drawing, and not an image of a tested product.

How Is “Medium” Filtration Defined?

Different rating systems involve different test methods; hence the ratings are not interchangeable. EN 779 was the general ventilation standard in Europe. Although it is now out of use, it had graded filters from G1 to F9 based on reported efficiency and average arrestance based on a predetermined particle size [7].

The new standard, ISO 16890, defines particulate matter efficiency as ePM1, ePM2.5, and ePM10 [1]. On the other end of the spectrum, ASHRAE 52.2 determines the MERV rating on a scale of 1 to 16 based on size-resolved efficiency after a conditioning step [8].

Since the testing and reporting procedures differ in eACH case, it is impossible to compare a legacy F7 rating with a MERV 13 rating. Actual grades must come from the individual filter's own test report.

Table 1: Rating systems for general ventilation filters.

Where Are Medium Filters Used in HVAC and Cleanrooms?

Medium-efficiency HVAC filters serve as the primary filters in commercial HVAC systems and as pre-filters before moving into HEPA filters in cleanrooms, hospitals, pharmaceutical facilities, and electronic installations. They act to prevent the total accumulation of particulate pollution at the next filtration level by providing protection of coils, ducts, and terminal filters.

How long the pre-filter will prolong the life of the HEPA filter depends on multiple conditions. It depends on the number of particles in the air, the amount of the airflow, the total time of service, dust properties, and the last pressure drop point. A percentage reduction in the amount of mass captured does not imply exactly the same percentage increase in the life of the filter.

To illustrate this, take a case where a HEPA filter in a certain system reaches its maximum resistance after 12 months without pre-filtering. Using medium filtration would provide an increase to that period; however, the actual increase must be determined from the pressure drop readings, operating conditions, and change-out practices of the establishment in question.

Which Materials Make Up the Filter Media?

The predominant four kinds of medium filter materials used for medium air filter media are fiberglass, synthetic polymers, cellulose, and different combinations of these materials. Type of fiber does not guarantee the evaluation of efficiency, pressure drop, and service life.

Other characteristics of the medium air filter media contributing to final performance include fiber diameter, bulk density, depth of filter medium, geometry of pleats, and the utilization of electrostatic charge effects. Fiber type alone does not establish efficiency, resistance, or capacity.

Physical form plays a role alongside chemistry. Pleated medium filters develop higher surface area within a fixed face size. Bag filters use sewn or welded pockets to produce a similar result, which is why pleated medium filters and bag types are not directly interchangeable.

V-bank packs fold a pleat segment into a thin, compact structure through which air is processed, in the same way pleated medium filters are folded. Form affects resistance and dust holding capacity in synthetic filter media, whereas chemistry defines temperature and moisture limits.

Example calculations utilizing specific catalogue values illustrate the extent of the effect. For one combined high efficiency model, based on Deiiang catalogue data, the face has a size of 592 x 592 mm and 20.04 m2 of filtering area. Area of the face = 0.592 x 0.592 = 0.3505 m2.

Hence, 20.04 / 0.3505 = approximately 57.2. However, this ratio holds true only in case the catalogue uses the same meaning of filtering area, therefore it is necessary to double check whether the data is about total area of pleat face, area of one side of the pack, or area of flat filtering medium.

Table 2: Comparison of medium filter media by material, strengths, limitations, typical applications, and datasheet verification points.

The table compares the four media families on the criteria that matter at selection. It is a conceptual illustration and not a digital photograph of a specific product.

Fiberglass and Cellulose Filter Media

Fiberglass air filter media is made by taking molten glass that has been spun into fibers and forming it into a mat. Typically, fiberglass air filter media diameter values reported by suppliers range from less than 1 µm to several µm depending on the grade and manufacturing route. Finer fibres increase surface area per unit mass, which allows capture without an excessively thick media layer.

The temperature capability of fiberglass air filter media exists at the finished filter level and not at glass as a material. The Deiiang catalogue shows one glass fibre bag filter family with a maximum operating temperature of 150 °C. Other Deiiang models show 70 °C for the combined high-efficiency filter and the DOP integrated filter. The final figure is often limited by the binder, sealant, and frame.

Cellulose media are produced from wood pulp or other plant fibres and sit below fiberglass air filter media on cost. They have a lower cost than glass or synthetic media and perform satisfactorily for dry, light-duty HVAC duty. Moisture is their biggest risk, as cellulose fibres can swell when wet and lose tensile strength, which shortens their service life in humid airstreams.

Synthetic and Blended Filter Media

Synthetic filter media employ polymers such as polyester, polypropylene or acrylic. Many grades of synthetic filter media are electrostatically charged and this raises initial efficiency with little or no added pressure drop. Charge-assisted performance is material specific and can be impacted by exposure to oils, aerosols, moisture or other contaminants. The extent of decay depends upon formulation, the contaminant, concentration and exposure time.

Purchasers who rely upon charge-assisted synthetic filter media should ask for efficiency data that has been measured after conditioning, or after the relevant exposure, where the manufacturer provides it. Without conditioned data, the clean-media efficiency value may misrepresent anticipated performance by overstating performance in an oily or humid system.

Blended media combine several types of fibres to optimize cost and performance. For instance, coarse polyester fibres are used in conjunction with finer fibres in order to give better particle capture efficiency with reduced cost. The blend ratio allows placement of the medium on an efficiency scale, but nothing is conclusive without obtaining a test report.

How Do Filter Media Materials Affect Performance?

Medium filter materials directly impact three closely tied variables: particle capture efficiency, airflow resistance, and dust holding capacity. These variables interact; therefore no single property of the medium air filter media is solely responsible for performance.

Fibre diameter, packing density, medium thickness, charge type, and pleat design all alter the balance between capture and resistance performance. Making a fair comparison between two different medium filter materials requires having a common standard.

Compare the medium filter materials' initial pressure drop under the same rated airflow and dimensions of the filter. Compare the efficiency level under the same standard. Compare the final resistance and the dust-loading conditions applied.

This original conceptual chart shows how fibre diameter and packing density shift resistance as dust accumulates. It is illustrative and does not represent measured test data.

Filtration Efficiency and Particle Capture

The medium air filter media employ interception, impaction, and diffusion in order to catch particles. Interception is the capturing of particles that follow the airstream but pass close enough to touch a fibre. Impaction captures larger particles which cannot follow through the medium that the airstream is following.

Diffusion is the capturing of extremely small particles whose erratic movement enables them to get into contact with the fibres. Fibre diameter influences which mechanism dominates.

Electrostatic charges on synthetic filter media give rise to a fourth means of filtration through Coulombic attraction. This means that charge-dependent ratings require conditioning data of efficiency, so that the user or consumer can make comparisons of these filters against mechanical filtration systems of identical nominal sizes.

Airflow Resistance, Dust-Holding Capacity, and Service Life

Initial pressure is utilized to refer to the measure of resistance of any clean filter at a standard temperature. Deiiang catalogues show that initial pressure is less than 50 Pa for F5 and less than 100 Pa for F8 for the 592 mm x 592 mm x 381 mm six-bag filter at the rated capacity of 2050 m3/h, with 3.18 m2 of material area and a final resistance of 250-400 Pa.

These values represent one bag-filter family. The dust-holding capacity of about 1200 g shown in the Deiiang catalogue is for a different, high-efficiency family: the 2500 m3/h combined grade with a media area of 20.04 m2. Therefore it is not proper to make comparisons between the two systems.

The reference to final resistance is just a set change-out value for the medium filter materials, not a material property. It has been determined by the designer, taking into account the pressure produced by the fan. Although media area can influence the loading capabilities of the media, it cannot do so by itself, due to the impact of dust characteristics and airflow on the loading pattern.

A simple fan-energy estimate helps compare options when assumptions are stated. Air power in watts is approximately the product of air volume in cubic metres per second times the pressure differential in Pa, divided by fan efficiency. Using 0.57 m3/s and 100 Pa, the air power is 57 W before efficiency losses. This is an estimate and not a verified saving.

What Materials Are Used for Frames and Support Components?

Frames and supporting elements do not play a role in filtering air, but HVAC medium filter construction relies on them to define whether the medium functions as intended. A frame that warps changes pleat spacing, and a failed gasket creates a bypass path around the medium filter materials. This is why HVAC medium filter construction treats frame, media, spacers, face guard, sealant, and gasket as one system.

In the procurement process, different materials will be used for HVAC medium filter construction, covering frames and supporting elements. Table 3 provides a comparison of all parts, including sealants and gaskets, because all of them contact the airstream.

Table 3: Frame, support, and sealing components in medium filter construction.

This original diagram identifies the frame, spacers, face guard, and gasket, illustrating how each part contributes to the media pack's support.

Frame Materials and Their Environmental Suitability

Galvanized steel frames are ideal for general HVAC medium filter construction where strength and affordability are crucial. The zinc coating helps protect against rust from exposure to the atmosphere.

Aluminum frames offer a lighter weight and excellent corrosion resistance, making them suitable for cleanroom air filter materials as well as situations where minimizing weight is important. According to data from Deiiang's catalog, there is an option for an aluminum folding frame or a galvanized frame in some models within their DOP integrated filter line.

Plastic frames made from materials like ABS or polypropylene provide corrosion resistance, serve as electrical insulators, and are common in synthetic filter media products. However, their maximum operating temperature varies based on specific grades and designs; therefore broad assumptions about plastic performance should not apply universally across different products.

Coated board frames work well with lightweight commercial filters and those designed for single use, but are not suitable for wet airflow conditions.

Supports, Separators, and Sealing Materials

Separators maintain pleat spacing to ensure that air flows through the entire media area effectively. Earlier versions featured aluminum foil separators that could add unnecessary weight and susceptibility to corrosion. Nowadays, many modern designs have moved away from traditional aluminum separators in favor of thermoplastic spacers, typically constructed from EVA hot-melt materials.

According to information provided by Deiiang's catalog, their high-efficiency filter model utilizes a separator-free design along with thermoplastic EVA spacers that maintain consistent pleat spacing throughout the surface area. Face guards play a vital role in safeguarding the media during handling processes; several models listed in Deiiang's catalog include coated expanded-metal face guards.

Sealants secure the media pack firmly to the frame. Deiiang catalog information denotes PU two-part polyurethane and EVA or neoprene gaskets. Silicone-free gaskets are mandated if silicone pollution is a point of process risk.

How Do Operating Conditions Affect Material Selection?

Operating conditions frequently determine the medium filter materials available more so than the efficiency goal does. A more constructive approach is determining processes instead of hard and fast rules.

Determine the greatest continuous and intermittent temperature ranges, level of humidity and possible condensation, chemical exposure, and cleaning or washdown schedule. Lastly, check that the finished filter meets the declared capacity.

This original diagram maps each operating condition to the material questions it raises, forming a selection sequence rather than a pass-or-fail checklist.

Humidity, Temperature, and Chemical Exposure

In most cases temperatures present the most transparent limitation. The Deiiang catalog states that the maximum allowable temperature for the combined high-efficiency filter and DOP integrated filter is 70 °C, and 150 °C for glass fiber bag filter materials. These limits are for finished filters listed by the manufacturer, not universal properties of materials.

Do not apply universal statements regarding humidity. The Deiiang catalog stipulates 80% relative humidity for the combined high-efficiency filter and DOP integrated filter, and up to 100% for the glass fiber bag filter family. The frame alone may not have been tested under any humidity condition.

Moisture resistance largely depends on the type of media, any treatments utilized, and the airstream condition. Confirm the limit stated by the manufacturer for the specific model, and if moisture is continuously present, favour moisture-tolerant construction.

Chemical compatibility cannot be determined from frame material alone, because it also involves sealants, gaskets, and media treatments that come into contact with the airstream. Consult the manufacturer for compatibility information pertaining to every wetted component at the required concentration and temperature.

HVAC and Cleanroom Operating Requirements

Medium-efficiency HVAC filters in commercial systems typically work at moderate temperature and humidity, which gives synthetic filter media with an aluminum or galvanized frame its advantage. According to Deiiang selection guidelines for use in common commercial space, the recommendation is MERV 8 to MERV 11 or F5 to F7 grades, as published in the current catalog.

Cleanroom air exchange rate is not a requirement set by iso 6. The air exchange rate is determined by process, occupancy, heat load, and contamination generation, and verified through validation procedures. iso 14644-1 specifies air cleanliness by particle concentration only [6]. unidirectional airflow can only be publicly stated where the project documentation verifies it.

The cleanroom air filter materials chosen set the pressure drop for filters, which affects fan energy regardless of air exchange rate, as the fan has to work against this resistance. Reducing the initial resistance will reduce the air power requirement at a given airflow, although the actual savings will depend on fan configuration, control strategy, and load profile.

How Do Medium Filter Materials Compare Across Applications?

More than any single specification, it is the application that defines the combination of medium filter materials used. A hospital air handling unit, a pharmaceutical pre-filtration system, and a high-temperature industrial process involve different sets of efficiency, temperature, humidity, and budget constraints.

In Table 4, medium-efficiency HVAC filters and their applications are compared directly. HEPA and ULPA filters are not medium filters and are excluded here; their materials are described later, only to show how construction changes at higher efficiency.

Table 4: Medium-filter application selection by media, frame and support, operating conditions, and verification points.

The diagram is a grouping of different combinations of materials with respect to their specific duty. It is for illustrative purposes only and not a product selection guide.

Material Combinations for HVAC Systems

For general HVAC duty the common media used are charged synthetic media or filter media in panel or bag form. Deiiang has catalogued a medium-efficiency chemical fiber bag filter rated at 1000 m3/h in F6, F7, and F9 grades, together with a fiberglass bag filter rated at 1700 m3/h in F5 and F8 grades.

Also listed are the W-bank medium combined filters in 23 x 23 x 11.5 inch F7 and 11.3 x 11.3 x 11.5 inch F8 configurations. Deiiang also lists a combined activated carbon medium filter rated at 3700 m3/h for gaseous and odour duty. These are manufacturer-published specifications.

Material Combinations for Cleanroom and Specialized Systems

For cleanroom air filter materials in pre-filtration duty, normally medium filters of the same family as HVAC applications are used, except with a more stringent level of verification. For medical, pharmaceutical, and electronics facilities, Deiiang has indicated which filters to use ahead of the HEPA stage, pointing to MERV 11 to MERV 13 or F7 to F9 grades.

On the other hand, terminal high-efficiency filters switch to the use of ultrafine filter paper, thermoplastic spacers, PU sealant, and extruded aluminum or plastic frames. Deiiang lists H13 efficiency rates of 99.97-99.99% at 0.3 µm and H14 of 99.995-99.999%. These products are not medium filters and are rated under EN 1822 [2].

How Should Buyers Verify Filter Specifications and Standards?

Buyers must verify through three avenues of information: the standard of filtration that the filters went through, catalog data on the specific model being purchased, and the filtration test certificates for that exact filter that gets delivered. If a specification states a standard without any model-level data, the standard cannot be enforced through delivery or compared from vendor to vendor.

This flowchart provides a step-by-step overview of the verification process, from defining the application and its material questions, through requesting model-level data and checking the standard, to piloting a sample and recording the batch reference.

Which Standards Apply to Medium Filters?

Reference to ISO 16890 means there are new standards now used instead of EN 779 by which to measure general ventilation filters. EN 779 now only provides historical context and not current standardization, which now necessitates using ISO 16890 and ASHRAE 52.2 if MERV is to be referenced [1] [7] [8].

Standards EN 1822, ISO 29463, IEST-RP-CC001, and MIL-STD-282 can be referenced for high-efficiency filters and their applicable tests and methods, and not for medium-efficiency HVAC filters used in general ventilation [2] [3] [4] [5].

ISO 29463 is a related international standard, but stating it is directly interchangeable with EN 1822 is an oversimplification of the relationship between the two documents. Buyers should review the applicable edition of whichever standard appears in the quote.

Table 5: Applicability of standards relevant to filter specification.

What Product Data Should Buyers Confirm?

The following lists the information that should be verified by buyers to compare medium-efficiency HVAC filters on an equal basis. All data points must refer to a particular product sheet and revision date. The method of conditioning is determined by the standard requested.

Two important aspects must be highlighted. Airflow and pressure drop must be assessed under identical circumstances and parameters, since resistance figures without a specified airflow cannot be compared. Media area can affect loading capacity but does not define it by itself.

How Can Deiiang Filter Materials Be Evaluated in a Real Project?

This case presents performance information documented by project personnel. It has not been verified as an independent result. The product data referenced here is taken from Deiiang catalog information, which consists of published manufacturer specifications.

This image is a general illustration of the product type and not a photograph of the specific project discussed below; it does not by itself demonstrate performance.

Project Conditions and Material Selection Challenges

This location is a pharmaceutical packaging cleanroom, positioned in an undisclosed location and designed to achieve ISO 6 status. According to the project group, they noted a high ambient particle load, a small space for the plenum area above the ceiling grid, and a strict restriction on filter pressure drop through the terminal stage.

The ceiling space limitation impacted the choice of the filter type to be used. The need to use deep filter packs would have required reducing the ceiling space and the amount of filter area. The pressure-drop limitation constrained media choice, as a higher-resistance medium raises fan duty at the same airflow.

The influence of the particle load is another limitation. When there is a high ambient load, terminal filter lifespan is shortened unless there is pre-filtration treatment of the particulates entering the flow stream. In this case, there was a need for a pre-filter stage that would lower downstream particulate load without creating an unnecessary pressure drop across the system.

Deiiang Solution, Installation, and Verified Results

Deiiang supplied low-profile H14 high-efficiency combined filters measuring 592 mm by 592 mm by 292 mm, delivering an air flow rate of 2500 m3/h and having 20.04 m2 of filtration area, with initial resistance of 220 Pa or lower, according to catalog data. The installation included silicone-free gaskets and pre-filters of class F7.

According to the team, the performance of every terminal filter was confirmed through DOP scan testing prior to putting it into operation. The team explained that particle counts were adjusted from an iso 7 baseline level to stable ISO 6 post-deployment. As there was no third-party measurement of fan energy, no energy saving figure is claimed.

Table 6: Project-reported case summary.

Frequently Asked Questions

What materials are medium filters made from?

The direct answer to "what are medium filters made of" is that most medium general ventilation air filters are constructed of fiberglass, synthetic polymer fibers, cellulose, or a combination of them. The frame may be made out of galvanized steel, aluminum, plastic, or coated board. Spacers, face guards, sealants, and gaskets may be made out of thermoplastic, metals, polyurethane, and rubber.

Are medium air filters made from fiberglass or synthetic media?

Yes; both are widely used, depending on their purpose. Fiberglass air filter media guarantees steady mechanical efficacy while providing a higher level of temperature tolerance in some cases. Synthetic filter media enables lower resistance because of electrostatic charge, which can be affected by oils, aerosols, and damp air.

What materials are used in a medium filter’s frame?

Galvanized steel suits general HVAC, aluminum suits cleanroom and weight-sensitive duty, and plastic suits humid or chemically aggressive environments. Coated board suits light commercial and disposable filters. Verify the frame together with the gasket and sealant, because all three contact the airstream.

What supports the filter media inside a medium filter?

A medium filter has built-in spacer supports, and in many cases thermoplastic material is used in hot melt form. Some pleated medium filters are designed so the media pack itself carries the main support. The filter face guard is built from coated expanded metal or plastic diamond mesh.

Do medium filter materials affect filtration performance?

Yes, but not in isolation. The medium air filter media properties, namely fibre diameter, packing density, media depth, charge state, and pleat geometry, all influence efficiency, resistance, and dust capacity. Compare products under the same test standard, airflow, and dimensions, and use the filter's own test report rather than the material name.

How should I choose materials for a medium filter in a cleanroom or HVAC system?

The first step is determining the purpose of the filter: primary HVAC filter, or pre-filter ahead of HEPA. Next, state the required classification, airflow, dimensions, and environmental conditions, including humidity, condensation, chemical exposure, and washdown routine. Validate all of this against the filter test report and change-out criteria.

References

• [1] ISO 16890-1:2016, Air Filters for General Ventilation — Part 1: Technical specifications, requirements, and classification system based upon particulate matter efficiency (ePM). International Organization for Standardization.
• [2] EN 1822-1:2019, High Efficiency Air Filters (EPA, HEPA and ULPA) — Part 1: Classification, performance testing, marking. European Committee for Standardization.
• [3] ISO 29463-1, High-efficiency filters and filter media used for particle removal from air — Part 1: Classification. International Organization for Standardization. Verify current edition.
• [4] IEST-RP-CC001, HEPA and ULPA Filters. Institute of Environmental Sciences and Technology. Verify current edition and the filter levels stated in that edition.
• [5] MIL-STD-282, Method 102.8, DOP-smoke penetration of aerosol filter elements. United States Department of Defense Test Method Standard. Verify current revision and customer acceptance requirements.
• [6] iso 14644-1:2015, Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness by particle concentration. International Organization for Standardization.
• [7] EN 779:2012, Particulate Air Filters for General Ventilation — Determination of the Filtration Performance. European Committee for Standardization. Withdrawn and superseded by ISO 16890.
• [8] ASHRAE Standard 52.2, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. ASHRAE. Verify current edition.