Bacterial Filtration Efficiency (BFE) Testing of Packaging Materials

Bacterial Filtration Efficiency (BFE) testing is a laboratory method used to quantify how effectively a material blocks aerosolized bacteria, and it has become an essential performance indicator for packaging materials used in medical, pharmaceutical, and hygiene applications. Conducted in accordance with recognized standards such as ASTM F2101 and EN 14683, the test challenges specimens with a controlled aerosol of Staphylococcus aureus and reports the percentage of bacteria captured by the material. This article explains the technical principles, sample types, test items, methods, and typical applications of BFE determination for packaging materials.

Technical Overview

Bacterial filtration efficiency (BFE) measures the capability of a porous material to act as a microbial barrier against bacterial aerosols. Although the method was originally developed for medical face mask materials, it is now widely applied to packaging materials, including nonwoven fabrics, sterilization pouch substrates, breathable films, and sterile barrier components for medical devices, wherever microbial barrier performance must be demonstrated and documented.

During the test, a controlled bacterial aerosol of Staphylococcus aureus (ATCC 6538) is drawn through the test specimen at a constant flow rate of 28.3 L/min (one cubic foot per minute). Bacteria that penetrate the material are collected on nutrient agar plates, incubated, and counted as colony forming units (CFU). The BFE value is calculated as the percentage reduction in CFU compared with a control run performed without a specimen. The principal reference standards include ASTM F2101, EN 14683 (Annex B), ASTM F2100, and the Chinese national and industry standards GB 19083 and YY 0469, which follow a similar technical principle.

Testing Samples

Nonwoven Fabrics and Composite Structures

Spunbond polypropylene, meltblown polypropylene, and SMS (spunbond-meltblown-spunbond) composites are the most frequently tested packaging substrates. These materials are used for mask packaging bags, surgical kits, instrument wraps, and protective liners where bacterial barrier properties are a functional requirement.

Sterile Barrier Packaging Substrates

Medical-grade paper, flash-spun high-density polyethylene sheet, and coated nonwovens used in sterilization pouches and hospital packaging rolls can be evaluated for bacterial filtration performance as part of sterile barrier system qualification and incoming material control.

Breathable Films and Laminates

Microporous breathable films and film-nonwoven laminates used in medical and hygiene packaging can be tested, although the pressure drop across less permeable materials must remain within the operating range of the test apparatus.

Functional Packaging Components

Filter media, breather patches, and vent membranes integrated into packaging systems for terminally sterilized products are also suitable candidates for BFE determination, since their function depends directly on microbial retention.

Testing Items

Typical test items offered by accredited third-party laboratories for packaging materials include:

• Bacterial filtration efficiency (BFE, %) at the standard challenge level of approximately 1.7 × 10^3 to 3.0 × 10^3 CFU per test
• BFE after temperature and humidity preconditioning to simulate storage and transport conditions
• Comparative BFE evaluation across production batches, suppliers, or material formulations
• BFE verification before and after sterilization processes such as ethylene oxide exposure or gamma irradiation
• Complementary tests frequently requested together with BFE, including differential pressure (breathability) and particle filtration efficiency (PFE) per ASTM F2299

Testing Methods

Specimen Preparation and Conditioning

Specimens are cut to fit the aerosol sampling apparatus and are conditioned prior to testing. Under ASTM F2101, specimens are conditioned at 21 ± 5 °C and 85 ± 5 % relative humidity for a minimum of 4 hours to normalize moisture content and ensure reproducible results. A minimum of five specimens per material is generally recommended to characterize average performance.

Aerosol Challenge Procedure

The test is performed using a biological aerosol chamber equipped with a nebulizer, a specimen holder, and a cascade impactor or agar collection system. The general procedure is as follows:

• Prepare a suspension of Staphylococcus aureus ATCC 6538 in tryptic soy broth and load it into the nebulizer.
• Generate a bacterial aerosol with a mean particle size of approximately 3.0 μm MMAD and deliver it through the system at a total airflow of 28.3 L/min.
• Run a positive control without a specimen to establish the challenge concentration, which should fall within 1.7 × 10^3 to 3.0 × 10^3 CFU.
• Clamp the specimen in the holder and challenge it with the aerosol, collecting downstream bacteria on tryptic soy agar plates.
• Incubate all agar plates at 37 ± 2 °C for approximately 24 to 48 hours and count the resulting colonies.

Calculation of Results

The bacterial filtration efficiency is calculated as BFE (%) = (C − T) / C × 100, where C is the average CFU recovered from the control runs and T is the average CFU recovered downstream of the test specimens. A material that recovers no colonies downstream yields a BFE of greater than 99.9 %, while results are typically reported to one decimal place.

Applicable Standards

• ASTM F2101: Standard test method for evaluating the BFE of medical face mask materials using a biological aerosol of Staphylococcus aureus
• EN 14683 (Annex B): European test method for BFE of medical face masks, widely referenced for barrier material qualification
• ASTM F2100: Performance specification that assigns BFE acceptance levels for materials used in medical face masks
• GB 19083.1 and YY 0469: Chinese standards specifying BFE requirements and test methodology for medical protective equipment materials

Applications

BFE test data for packaging materials support a wide range of industrial and regulatory purposes:

• Qualification of sterile barrier systems and support of conformity with ISO 11607 requirements for terminally sterilized medical device packaging
• Incoming material inspection and supplier quality control for converters of nonwoven and composite packaging rolls
• Regulatory submissions and technical documentation where microbial barrier evidence is required for mask packaging, hygiene product packaging, and related applications
• Research and development screening of new meltblown, composite, and breathable film structures intended for microbial barrier functions
• Stability and lot-release testing to verify that bacterial filtration performance remains consistent throughout production and shelf life

FAQ

What is considered a passing BFE result?

Acceptance criteria depend on the product specification. Common benchmarks include BFE ≥ 95 % for Type I materials under EN 14683 and BFE ≥ 98 % for higher-performance classes under EN 14683 and ASTM F2100 Levels 2 and 3. For packaging materials, the required limit is usually defined by the manufacturer or the end-use regulatory requirement.

How is BFE different from particle filtration efficiency (PFE)?

BFE uses a live bacterial aerosol with a mean particle size of about 3.0 μm and measures captured viable organisms, whereas PFE per ASTM F2299 uses inert submicron latex spheres. BFE reflects biological barrier behavior, while PFE characterizes fine particle retention; the two tests are complementary rather than interchangeable.

How many specimens are required for a valid test?

Most standards recommend a minimum of five specimens per material, together with valid positive controls within the specified challenge range. Additional specimens may be tested when characterizing variability across a production lot.

Can non-porous films be tested for BFE?

Dense, non-breathable films typically achieve near-total bacterial retention, but excessive pressure drop may prevent testing under the standard 28.3 L/min flow. In such cases, the material may be qualified through alternative barrier assessments or by testing at reduced flow with documented method deviation.

Do laboratory BFE results represent real-world performance?

BFE testing provides a standardized, reproducible measure of bacterial barrier capability under controlled laboratory conditions. It is suitable for material comparison, specification compliance, and quality control, but real-world performance also depends on packaging design, sealing integrity, and handling conditions.

Where can BFE testing of packaging materials be performed?

Testing should be performed by accredited third-party laboratories or qualified in-house microbiology facilities equipped with validated aerosol challenge apparatus, biosafety containment for Staphylococcus aureus handling, and competence in the relevant ASTM, EN, or GB test methods.