Textile Filter Media: Balance Particle Capture and Pressure Drop

Choose the filter around the process it must serve

A roll of filter fabric can look sound and still be wrong for a dust collector. Its fibres may suit the temperature but release dust poorly. Its test result may look excellent while a loose seal lets dirty air pass around it. A low price per bag says little about either problem.

Textile filter media must be assessed as part of a working system. The useful questions concern particle capture, airflow, pressure loss, cleaning and service life. Each answer needs a stated operating condition. A single efficiency number cannot settle the whole choice.

This guide focuses on textile filters that can be cleaned and used again to collect dry industrial dust. Original teaching examples show how fabric choice affects the collector. The values are fictional. They do not set design limits or emission limits. Nor are they approved settings for any machine.

Liquid filtration, mist removal and respiratory protection have different duties and tests. These products may contain fibres. That alone is no reason to transfer a result between these uses.

Start with the process, then work towards the fabric. Define what enters the collector, what must leave it and how the installation will be checked. This gives a supplier a useful problem to solve.

Separate fabric properties from collector performance

The medium is the porous material through which the gas passes. An element is the finished bag, cartridge or other assembly that holds that medium. The collector holds the elements, seals and supports. It also has equipment to clean the filters and remove the collected dust.

The wider extraction system also includes the hood, ducts and fan. A good filter cannot collect dust that never enters the hood. Local exhaust ventilation, or LEV, uses these parts as one system. The HSE guide to LEV explains how to design and maintain it. The guide also covers commissioning, which checks the installed system before use.

Keep those levels distinct when comparing evidence:

Ask what was tested, how it was tested and which item the report represents. A fabric sample from another production lot may be useful background. It is weaker evidence for the specific bags being supplied.

Understand how fibres capture particles

A fibrous filter does more than act as a sieve. A particle may be too large to pass through an opening. It may also hit a fibre because its inertia prevents it from following a bend in the airflow. Another particle may follow the flow but pass close enough to touch a fibre.

Very small particles also move randomly as gas molecules strike them. This motion can bring them into contact with fibres. These mechanisms are commonly called sieving, impaction, interception and diffusion. Donaldson explains them in its guide to particle capture in fibrous air filters.

Their importance depends on the particles, medium and flow. Do not turn a nominal pore size into a promise that all smaller particles will pass through. One quoted particle size does not prove capture across the full size range. The cited guide concerns sterile-air products. Its product rating is not a baghouse rating.

Before buying, ask for the measured efficiency or penetration. Check the conditions under which it was tested. Keep particle-size units intact. One millimetre equals 1,000 micrometres. A lost symbol can therefore change what the specification means.

Specify construction and service conditions together

Designers can choose woven fabrics, needlefelts or pleated media. Each offers a way to provide a porous structure and useful area. Their names alone do not establish which product will work best. Check the fibre, support and finish. The element shape and cleaning method also matter.

Donaldson's overview of industrial filter types distinguishes fabric bags, cartridges and pleated bags. It also describes different media choices for different gas conditions. Use this to understand the types on offer. Then ask for evidence about the proposed product.

Give the supplier the expected operating range, including starts, stops and unusual batches. Record gas temperature and moisture conditions. State which chemicals may be present. Add the dust loading and a description of the dust. A description such as “textile dust” is too broad to settle compatibility.

Ask whether the dust contains oil or finishing residues. Could another process add different material to it? Record the cleaning system and the exact element dimensions. The medium may suit the duty. Yet the finished element can still fail if it does not fit the collector.

Request product-specific limits and the conditions attached to them. A fibre's melting point does not set a safe temperature for continuous use. Check the limit for the finished filter. The complete element includes seams, seals and supports as well as the main fabric.

Start the chemical review with the available safety data sheets. ApparelDiary's guide to reading a safety data sheet explains what to look for. That sheet alone cannot prove that a filter will suit the process. It may not cover every property of the dust being collected.

Measure air permeability without confusing it with efficiency

Air permeability describes flow through the material under specified conditions. ASTM D737 provides a textile air-permeability test method. Its public scope includes woven and nonwoven materials. The guidance notes that construction and finish can affect results. The direction of airflow can also matter.

When comparing reports, first check the method and pressure difference. Then check specimen area, flow direction, conditioning and units. Two numbers cannot be compared fairly if one important test condition differs. Keep the original reports. A comparison sheet that shows only the largest value loses the test context.

A permeability result does not show how much dust passed through the specimen. That requires a particle test. A clean-fabric test has another limit. It does not show how the material behaves after repeated loading and cleaning.

Suppose two suppliers quote different airflow values but use different pressure differences. The first action is to request comparable tests. The larger number may reflect the test conditions. It need not mean that the product itself is more open.

Use permeability as one controlled property in the specification. Connect it to the required filtration and cleaning evidence. Do not assume that the most open fabric must be best. The densest fabric is not an automatic winner either. Both need evidence for the intended duty.

Calculate air-to-cloth ratio from the area actually available

Air-to-cloth ratio, also called face velocity, relates gas volume flow to filtering area. The EPA baghouse design chapter uses actual gas flow and net cloth area. Available area differs from total installed area. Some of the cloth may be offline while a compartment is being cleaned.

For consistent SI units:

Face velocity, m/min = gas flow, m³/min ÷ available filter area, m².

Consider a fictional collector receiving 6.0 m³/s at the conditions inside the collector. Its available filtering area is 500 m². First convert seconds to minutes:

6.0 × 60 = 360 m³/min.

Face velocity = 360 ÷ 500 = 0.72 m/min.

This is also 0.012 m/s. Neither result is a recommended operating value. It describes the chosen case and gives the supplier a clear basis for discussion.

Now assume the collector has four equal compartments. Each contributes 125 m². Now take one compartment offline in this teaching case. Keep the same total flow. Available area becomes:

500 − 125 = 375 m².

Face velocity during that condition becomes 360 ÷ 375 = 0.96 m/min. That is a rise of one-third, although the installed cloth area has not changed.

The last row is arithmetic, not permission to reduce extraction. A lower flow may fail to capture dust at the source. The required hood performance must remain part of any operating change.

Also check whether the flow is actual, standardised, wet or dry. An emissions report may show a normalised volume. This need not equal the actual volume passing through the cloth. State the reference temperature and pressure. Include the moisture basis and make any required conversion.

Read pressure loss as a trend with a known flow

Dust accumulates on the medium during service. Cleaning removes part of that deposit so filtration can continue. The EPA guide to fabric-filter monitoring lists useful indicators. These include pressure difference, gas flow and temperature. It also calls for attention to cleaning operation and outlet particle measurements.

The pressure reading needs its measuring points. A reading across the filter section covers that section. It may not equal the total pressure the fan must supply. Ducts, fittings and other components also contribute to the system requirement.

Record pressure loss alongside airflow and the stage of the cleaning cycle. A pressure rise at a steady flow raises a different question from the same rise during an increase in flow. A sudden low reading also deserves attention if outlet dust has increased.

Use a trend record with time, process state and flow. Add filter pressure difference and cleaning events. Add maintenance changes and unusual batches. This lets an engineer relate a new pattern to what actually changed.

Do not invent a universal replacement pressure from a generic article. Use the approved operating range and the evidence needed for that installation. A clean-looking graph is useful only if its sensors, units and process records are sound.

Link pressure loss to fan power on a stated basis

The US Department of Energy fan sourcebook explains gas power. It is the product of pressure rise and volume flow, with consistent units. It also distinguishes fan efficiency from the wider drive system. Keep those boundaries clear in an energy estimate.

For a low-pressure, steady-flow teaching model:

Electrical power, kW = Q × Δp ÷ (1,000 × η).

Here, Q is actual volume flow in m³/s. The pressure rise Δp is in pascals. The assumed combined efficiency η covers the fan, motor and drive. Its boundary runs from electricity input to gas power. It is not merely the fan's catalogue efficiency.

Use the same 6.0 m³/s flow. Suppose the filter pressure loss is 1,000 Pa and the rest of the required pressure rise is 1,400 Pa. Total required rise is 2,400 Pa. With an assumed combined efficiency of 0.65:

Electrical power = 6.0 × 2,400 ÷ (1,000 × 0.65) = 22.15 kW.

Now suppose filter loss rises to 1,600 Pa. Assume the controls keep the same flow. Combined efficiency stays at 0.65. Total required rise becomes 3,000 Pa:

Electrical power = 6.0 × 3,000 ÷ (1,000 × 0.65) = 27.69 kW.

The difference is about 5.54 kW. Across 4,000 hours at those unchanged conditions, it represents about 22,154 kWh. Calculate from unrounded values, then round the result.

This is a sensitivity example, not a promised saving. A fixed-speed fan may deliver less flow as resistance rises. Efficiency can also change with the operating point. Measure actual flow and electrical input before making a business claim.

Cleaning energy and maintenance costs belong in the assessment too. ApparelDiary's compressed-air cost guide explains why compressed-air demand needs a defined measurement basis.

Keep collection efficiency and outlet concentration visible

Collection efficiency compares the particle mass entering and leaving a defined boundary. The general mass-flow expression is:

Efficiency = 1 − (outlet particle mass flow ÷ inlet particle mass flow).

If concentrations and gas volume flows use matching bases:

Efficiency = 1 − (Cout × Qout) ÷ (Cin × Qin).

Only when inlet and outlet volume flows are equal on that basis does this reduce to 1 − Cout ÷ Cin. Leakage, added air or unlike gas-volume bases can invalidate that shortcut.

For an original example, assume equal flows of 6.0 m³/s. Inlet dust concentration is 900 mg/m³. Outlet concentration is 9 mg/m³. Then:

Efficiency = 1 − 9 ÷ 900 = 0.99, or 99%.

Inlet particle mass flow is 900 × 6.0 = 5,400 mg/s, equivalent to 19.44 kg/h. Outlet mass flow is 9 × 6.0 = 54 mg/s, or 0.1944 kg/h.

Both the efficiency and outlet concentration matter. The example's 9 mg/m³ is not an emission limit. A real requirement may use other reference conditions. It may also define an averaging period and a sampling method.

Record what the test measures. A total mass result does not describe capture at each particle size. A number-based particle result is also not the same as a mass-based result. Keep the method and its uncertainty with the reported value.

Compare the mass that passes through

Two high efficiency figures can look almost equal. The share that passes through often makes the difference easier to see. In a separate comparison, let one medium remove 99% of the incoming mass. Let another remove 99.9% under the same test conditions. These figures are assumed for the example; they are not measured product claims.

The first medium lets 1% of the mass pass. The second lets 0.1% pass. The second share is one-tenth of the first. The gain is 0.9 percentage points in removal, but a tenfold drop in the mass passing through.

With 900 mg/m³ at the inlet and equal inlet and outlet gas flows, the two outlet values would be 9 and 0.9 mg/m³. Keep the same flow basis and test method for both. This comparison cannot tell you the pressure loss, cleaning needs or service life. Those still need their own evidence.

Show why a small bypass can dominate the result

Consider a separate simplified mixing example. Assume the medium removes 99.9% of particle mass from the gas that passes through it. One percent of the incoming gas bypasses that medium completely. Both streams start with the same dust concentration and mix at the outlet.

The fraction passing through the medium is 0.99. Its penetration fraction is 0.001. Total penetration becomes:

0.01 + (0.99 × 0.001) = 0.01099.

Overall collection efficiency is therefore:

1 − 0.01099 = 0.98901, or 98.901%.

At an inlet concentration of 900 mg/m³, the mixed outlet would be 9.891 mg/m³. With no bypass, the assumed medium alone would produce 0.9 mg/m³. The small bypass has changed the outcome substantially.

This is a teaching model, not a diagnosis of an actual leak. The flow shares are assumed known. Inlet concentration is equal in both streams. There is no other particle source or loss. Real leakage needs investigation using suitable methods.

The purchasing lesson is practical: inspect the complete sealing arrangement. Record the element dimensions, seating method, assembly condition and installation checks. Buying a better medium cannot by itself correct an open path around it.

Use a test standard for the question it addresses

ISO 11057:2011 compares media used to filter dry gas. The media can be cleaned by a pulse of air. Its public scope states a key limit. These tests do not predict absolute performance at full scale. A report can help with selection. It does not guarantee the proposed installation.

ISO 16313-1:2025 covers a different test. It is a laboratory test for small dust collectors. The units have built-in fans and use pulses of air to clean the media. Its scope excludes mist and fume collectors. It tests how the collector works under simulated conditions. The scope states that this does not guarantee system performance.

These scopes help a buyer ask for the right evidence. They do not supply an automatic pass limit for every factory. Agree the requirement, test method, operating conditions and acceptance rule before testing.

When a report names a standard, check its edition and the tested item. Ask about deviations, sample preparation and the test conditions. Read the result as a whole, including limitations. A standard number on a cover page is not enough.

Keep laboratory comparisons separate from site acceptance. The first can help choose a candidate. The second checks the installed system. Does it do the required job under the stated conditions?

Plan a trial that can explain the result

Before changing media, record the baseline with the existing process. Include representative operating periods rather than choosing only the quietest shift. Preserve the old specification and maintenance history so differences can be traced.

Define the candidate by product code, lot, construction and element drawing. State which system settings will stay fixed. List any changes the approved procedure allows. Suppose flow, cleaning and media all change together. The result then cannot be attributed to the fabric alone.

Use the same measurement methods before and after the change. Check that instruments are suitable and their calibration status is known. Record sensor locations and units so another person can reproduce the comparison.

The table identifies questions, not proven causes. Preserve samples and records before changing several settings. Follow the equipment's safe isolation and maintenance procedure when inspection requires access.

Set the release decision before the trial. It should cover extraction performance, outlet results, pressure behaviour, cleaning and product compatibility. A short trial may leave service life unresolved. State that limit. Do not predict a replacement interval without evidence.

Address dust hazards separately from filter efficiency

Good particle capture does not prove that a collector is safe for combustible dust. OSHA's combustible-dust guidance explains the hazard. Finely divided combustible material can explode under suitable conditions. Its examples include materials and processes relevant to textiles.

Use competent assessment of the actual dust and installation. Controls may need to address ignition sources as well as the fabric. The collection equipment and connected process also need review. “Antistatic” describes one product property. It does not establish a complete design for explosion protection.

Test and clean the equipment without spreading hazardous dust into the workplace. Keep inspection, replacement and disposal within the site's approved procedures. Requirements depend on the material, location and installation.

Respiratory protection is a separate decision. NIOSH explains how to identify approved respirators, including checking its Certified Equipment List. A textile medium may have an efficiency claim. That does not make an improvised face covering an approved respirator.

Keep the decision useful after installation

Save the selected specification, reports, installation checks and trial results together. The record should show why the medium was chosen and the conditions under which it was accepted. This makes a later process change easier to assess.

When a supplier proposes a replacement, compare more than fibre names. Check dimensions, support, surface treatment, test evidence and compatibility with the existing collector. A familiar product label can conceal a material change.

Use trends to guide maintenance while retaining the required planned tasks. ApparelDiary's preventive and predictive maintenance guide explains how those approaches support different decisions.

The strongest filter choice connects the fabric to measured system performance. Keep airflow, pressure, particle results and cleaning conditions together. A change in one value then gives you a question to investigate. Use that evidence to decide whether another bag is needed.

References

• HSE: Controlling airborne contaminants at work, HSG258. System design, commissioning and maintenance guidance.

• Donaldson: particle-capture mechanisms in fibrous air filters. Mechanisms only; sterile-air ratings are not transferred to baghouses.

• Donaldson: industrial dust collector filter types. Product constructions and application distinctions.

• ASTM D737-18(2023): Air Permeability of Textile Fabrics. Public scope and significance of the test.

• US EPA: Baghouses and Filters, Control Cost Manual chapter. Gas-to-cloth ratio and net-area principles; historical cost figures are not used.

• US EPA: Monitoring by Control Technique—Fabric Filters. Operating and outlet-performance indicators.

• US Department of Energy: Improving Fan System Performance. Flow, pressure, efficiency and fan operating points.

• ISO 11057:2011: filtration characterisation of cleanable filter media. Public scope and limits of media-test interpretation.

• ISO 16313-1:2025: laboratory testing of dust collectors with integrated fans. Public scope and limits of collector-test interpretation.

• OSHA: Combustible Dust—An Explosion Hazard. General hazard background.

• NIOSH: Identifying Approved Respirators. Respirator approval and identification.