Introduction

Pore size is one of the most important specifications when choosing a membrane filter. However, despite its importance, many users misunderstand what pore size truly represents and how it affects filtration performance. These misconceptions can lead to incorrect filter selection, reduced efficiency or unreliable results.

This article addresses the top five misconceptions related to membrane pore size and provides clear explanations to help users make better decisions.

1. Misconception: “Pore Size Is a Single Exact Value”

Many users assume that membranes have one fixed pore size, such as “0.22 μm.” In reality, membranes have a distribution of pore sizes.

• Pore size rating represents the nominal or maximum effective pore size
• Real membranes exhibit a range based on material and manufacturing methods
• Pore size distribution affects retention behavior and flow rate

Understanding this helps explain why different materials with the same rated pore size may behave differently.

2. Misconception: “Smaller Pore Size Is Always Better”

Choosing smaller pores doesn’t always improve results. In fact, it can negatively impact performance.

• Smaller pores mean significantly lower flow rate
• Higher backpressure may damage sensitive samples
• Unnecessarily small pores can increase filtration time and cost

The best pore size is the one that meets retention requirements without compromising efficiency.

3. Misconception: “Same Pore Size Means Same Performance Across Materials”

A 0.45 μm PES membrane does not behave the same as a 0.45 μm PTFE or Nylon membrane. Material structure matters.

• Different surface energies affect adsorption
• Internal pore geometry differs (sponge-like, fibril, asymmetric skin)
• Hydrophilicity or hydrophobicity influences flow behavior

Thus, pore size alone cannot predict real-world filtration performance.

4. Misconception: “Bubble Point Equals Pore Size”

While bubble point correlates with pore size, it does not directly measure it.

• Bubble point reflects the largest effective pore, not the full distribution
• Different wetting liquids produce different bubble points
• Surface tension and contact angle heavily influence results

Bubble point is a valuable QC tool, but not a complete pore size characterization.

5. Misconception: “Rated Pore Size Determines All Retention Behavior”

Retention depends on more than just pore size.

• Electrostatic interactions can enhance or reduce retention
• Surface chemistry affects adsorption
• Roughness influences fouling and trapping
• Depth structure affects how particles are captured

Two membranes with the same pore size can show very different retention efficiencies depending on their structure and material.

Conclusion

Understanding membrane pore size requires more than reading a number on a specification sheet. By recognizing key misconceptions—such as the idea that pore size is exact, universal or solely predictive of retention—users can make more informed decisions and optimize their filtration process.

Purchase Suggestion

We provide membrane filters with well‑characterized pore size and detailed performance data. Contact our technical experts to find the right pore size and material for your specific application.