Hydrophilic vs. hydrophobic membranes: which one should you use?

What the terms mean

A hydrophilic membrane readily wets with water and aqueous solutions, allowing them to pass through under normal pressure or vacuum. A hydrophobic membrane repels water—an aqueous sample won't pass through it without significant force, pre-wetting with a compatible solvent, or a hydrophilic surface treatment.

When you need hydrophilic

Any aqueous sample—buffers, media, water samples, most biological fluids—needs a hydrophilic membrane (or a hydrophilic-treated variant of an otherwise-hydrophobic material like PTFE or PVDF) to filter without a fight. PES and nylon are inherently hydrophilic; PTFE and PVDF are naturally hydrophobic unless specifically treated.

When you need hydrophobic

Gas filtration and venting (allowing air through while blocking liquid or aerosols) is the classic hydrophobic use case—the membrane needs to resist wetting so it doesn't block gas flow. Hydrophobic membranes are also used for aggressive organic solvents where the material's inherent chemical resistance (like standard PTFE) matters more than aqueous wettability.

The common mistake

Ordering a hydrophobic membrane for an aqueous application—or vice versa—is one of the most common and avoidable filtration errors. It shows up as a filter that simply won't pass the sample no matter how much pressure or vacuum you apply. Always confirm wetting behavior against your actual sample type before ordering, not just the base material name.

Hydrophilic-treated hydrophobic materials

Many PTFE and PVDF products are available in hydrophilic-treated versions specifically to combine the material's chemical resistance with aqueous compatibility—useful when you need both properties. Confirm which version you're ordering; the base material name alone doesn't tell you.