The micron rating on a filter bag tells you the particle size the bag is designed to capture — but two bags marked “10 micron” can perform very differently, because the number alone doesn’t say how completely particles at that size are removed. Here’s what the ratings actually mean and how to choose one.
Nominal vs. Absolute
Nominal ratings — standard for felt filter bags — mean the media captures a majority of particles at the rated size on a single pass (typically 50–90% depending on the media). Particles keep getting captured as the cake builds, so real-world efficiency rises during the run. Absolute ratings mean a defined, tested cutoff (99%+ retention), which is cartridge and membrane territory — with the exception of monofilament mesh, whose woven openings are a true geometric cutoff: nothing bigger than the opening passes.
Common Micron Reference Points
| Particle | Approx. size |
|---|---|
| Beach sand | 100–1000 µm |
| Human hair | ~70 µm |
| Limit of naked eye | ~40 µm |
| White blood cell | ~25 µm |
| Talcum powder | ~10 µm |
| Red blood cell | ~8 µm |
| Bacteria | 0.5–2 µm |
Choosing a Rating
- Define the failure, not the wish. What particle size actually causes the downstream problem — plugged nozzles, visible haze, spec violation? Filter for that.
- Go loosest-that-works. Every step tighter shortens bag life roughly by half in dirty service. A 25-µm bag that gets changed on schedule beats a 5-µm bag that blows out early.
- Stage if needed. Heavy solids? Put a coarse bag (100–200 µm) ahead of the tight one and both last longer.
- Felt below 35 µm, mesh above when reuse matters. Felt covers 1–200 µm nominal; monofilament mesh covers 35–800 µm with a true cutoff and washability.
Not sure? Describe the fluid and the problem: 800-554-8555 or request a quote. We’ll recommend a rating and send a sample to prove it.