How capillary flow porometry works
What is capillary flow porometry
Capillary flow porometry is a characterisation technique used to measure the pore size and pore size distribution of through pores, where the wetting liquid is displaced from the pores of a porous material by applying pressurised gas. Gas-liquid porometry can cover the widest range of the through pores from 500 μm down to 18 nm. This technique can provide essential information about the porous structure of materials, and data which can be crucial for manufacturers to ensure pore uniformity and optimise performance.
How does the capillary flow porometry work?
The technique is based on the displacement of a wetting liquid from a porous sample by applying an inert gas.
P = (4γcosθ)/D, where:
γ = surface tension of the wetting liquid
θ = contact angle
D = pore diameter
A capillary flow porometer measures the gas pressure required to empty pores of specific diameters, which are then calculated using the equation mentioned above. The instrument also records the gas flow rate as a function of the applied pressure across the porous material. This data is further used to generate dry and wet curves. The wet curve is obtained by measuring the sample saturated with the wetting liquid, whereas the dry curve is recorded from the measurement of a dry sample. Both curves are further used to calculate the pore size distribution.
As a result, the capillary flow porometry provides information about the bubble point pore size, the mean flow pore size, the smallest pore size, cumulative and differential pore size distribution, and air permeability.
Two porometry techniques: Gas-liquid porometry and Liquid-liquid porometry
Liquid-liquid porometry (LLP):
A displacement liquid replaces the wetting liquid
Enables measurement of extremely small pores (0.5 µm – 2 nm)*
Ideal for ultrafiltration and nanofiltration media
Gas-liquid porometry (GLP):
Uses an inert gas to displace a wetting liquid
Flow rate is measured with a high-resolution gas flow meter
Suitable for a wide pore size range (500 µm – 18 nm)*
*Measurement range depends on the chosen liquid or liquid pair.
Applications across porous materials
Capillary flow porometry is widely used to characterize:
Polymeric membranes (flat sheet and hollow fiber)
Nonwovens and technical textiles
Ceramic membranes and tubes
Porous metal discs and metal fiber media
And other filter media having through pores.
These measurements help manufacturers validate pore uniformity, optimize performance, and meet strict industry specifications.
Technical note - Bubble point determination in capillary flow porometry
Read more about this in this technical note
Fully automated and user-friendly testing
Porometer is a leading provider of advanced instruments for pore size analysis. To measure the capillary flow porometry, Porometer offers advanced instruments like the POROLUX™ Cito and POROLUX™ Revo (gas-liquid porometers) and POROLIQ™ (liquid-liquid porometer). Our systems deliver:
The most accurate pore size and pore size distribution
Automated control and real-time software monitoring
A detailed sample analysis and data export
Why choose Porometer?
With decades of expertise in pore size analysis, Porometer provides precise, user-friendly instruments that meet the highest standards in filtration and material science. Whether you're in R&D, QA/QC, or production, our porometers ensure accurate, traceable, and repeatable measurements.
Explore our full range of porometers and learn how they can optimize your material characterization: Product overview
