Filter Integrity Test Calculator
How to use: Select your filter manufacturer and membrane, set the format and number of cartridges, then read the integrity test specifications. Toggle "Did my filter pass?" to enter measured values and get an instant pass/fail verdict with margin analysis.
Filter Manufacturer & Membrane
Filter Format
Number of Filters ?
Upstream Volume (mL) ?
Test Conditions
Temperature (°C) ?
Altitude (m) ?
Did my filter pass?
Enter measured values for instant pass/fail verdict
Test Type
Measured Bubble Point (mbar)
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Min Bubble Point (mbar)
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Max Forward Flow (mL/min)
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Max Pressure Drop (mbar)

Bubble Point vs Temperature

Full Test Specifications

ParameterValueUnitNotes

Manufacturer Specifications Reference

FilterPore (µm)MaterialMin BP (mbar)FF Pressure (mbar)Max FF/10" (mL/min)Ref Temp

About Filter Integrity Testing in Biopharmaceutical Manufacturing

Filter integrity testing is a mandatory requirement in GMP biopharmaceutical manufacturing to confirm that sterilizing-grade filters are intact before and after use. The four primary integrity tests are bubble point, forward flow (diffusive flow), pressure hold (pressure decay), and water intrusion. Each test evaluates the membrane from a different angle: bubble point detects the largest pore, forward flow measures cumulative diffusion across the entire area, pressure hold converts diffusion into a measurable pressure drop in the upstream volume, and water intrusion is specific to hydrophobic PTFE filters used for vent and gas filtration. For a comprehensive guide to each method, see the full article on filter integrity testing in bioprocessing.

This calculator provides manufacturer-specific specifications for filters from MilliporeSigma (Durapore PVDF, Express SHC PES), Pall (Supor EKV, Fluorodyne EX, Emflon PFR), and Sartorius (Sartopore 2, Sartobran P). It applies temperature corrections based on the surface tension of water at the test temperature using IAPWS reference data, and altitude corrections for the atmospheric pressure term in pressure hold calculations. Multi-cartridge scaling follows industry-standard rules: forward flow scales linearly with the number of cartridges, while bubble point is an intrinsic membrane property that does not change with filter area. The pass/fail mode gives an instant verdict with margin analysis, showing how close the measured value is to the specification limit.

Regulatory agencies including the FDA and EMA require post-use integrity testing of all sterilizing-grade filters. The filter integrity testing guide covers the regulatory framework, test selection, and troubleshooting common failures. For related GMP calculations, see the viral clearance LRV calculator and the endotoxin dilution calculator.

Related Articles

Filter Integrity Testing in Bioprocessing
Bubble point, forward flow, pressure hold methods explained
Viral Clearance Strategy
Nanofiltration and LRV calculations for biologics
Cleaning Validation in Biopharmaceutical Manufacturing
MACO methods, swab/rinse sampling, regulatory comparison
FDA Process Validation for Biologics
Complete guide to Stages 1-3 per FDA guidance

Frequently Asked Questions

What is the bubble point test for sterile filters?

The bubble point test measures the minimum gas pressure required to displace liquid from the largest pore in a wetted membrane. It is derived from the Young-Laplace equation: BP = 4γcosθ/d, where γ is the surface tension of the wetting liquid, θ is the contact angle, and d is the pore diameter. A filter passes if the measured bubble point exceeds the manufacturer's published minimum. For a 0.22 µm Durapore PVDF membrane water-wetted at 23 °C, the minimum specification is 3450 mbar.

How does temperature affect filter integrity test results?

Temperature primarily affects the surface tension of the wetting liquid. Water surface tension decreases from 72.74 mN/m at 20 °C to 69.59 mN/m at 40 °C (a ~4% drop), which proportionally lowers the bubble point. The correction formula is BPcorrected = BPref × (γT / γref). Higher temperature also increases gas diffusivity, raising forward flow readings. As a rule of thumb, bubble point changes by approximately 2% per 10 °C.

What is the difference between forward flow and bubble point tests?

The bubble point identifies the pressure at which liquid is displaced from the largest pore, detecting gross defects. Forward flow measures the rate of gas diffusing through the wetted membrane at a test pressure below the bubble point. Forward flow is more sensitive to distributed small defects because it sums diffusion across the entire membrane area. For multi-cartridge systems, forward flow scales linearly with filter area, while bubble point remains an intrinsic membrane property.

How do you scale forward flow limits for multiple cartridges?

Forward flow limits scale linearly with the number of cartridges. If one 10" cartridge has a maximum forward flow of 13.3 mL/min, a housing with 3 cartridges has a limit of 39.9 mL/min. Bubble point does NOT scale because it measures an intrinsic pore property. For pressure hold tests, total allowable diffusion equals single-cartridge diffusion multiplied by the number of cartridges, but the larger upstream volume of a multi-round housing partially offsets the higher total diffusion rate.

When should I use a pressure hold test instead of forward flow?

Pressure hold tests are preferred for large multi-cartridge housings (4+ cartridges) where a single defective cartridge could be masked by the total diffusive flow of the remaining integral filters. The test measures the pressure drop rate in the upstream volume. The acceptance criterion is: ΔPmax = (Dmax × T × Pa) / Vh, where Dmax is the maximum allowable diffusion, T is the test duration, Pa is atmospheric pressure, and Vh is the upstream system volume.

What is the water intrusion test for hydrophobic filters?

The water intrusion test (WIT) is designed for hydrophobic PTFE filters that cannot be water-wetted. Water is introduced upstream and pressurized. Because the membrane is hydrophobic, intact pores repel water, and only defects allow passage. The measured intrusion volume over a fixed period (typically 10 minutes after stabilization) is compared to the specification limit. WIT limits scale linearly with the number of cartridges, similar to forward flow.