Felt filter bags trap particles throughout the thickness of the media (depth filtration) at a nominal micron rating; mesh filter bags cut particles at a fixed pore opening on the surface (surface filtration) at a more precise absolute micron rating. Felt holds more dirt before it needs changing; mesh gives you a tighter, more repeatable cut point — and in many applications can be cleaned and reused. Which one is right for your process depends on your fluid, your particle load, and how precise the cut point needs to be.
Table of Contents
- What's the Difference Between Felt and Mesh Filter Bags?
- How Does Felt (Depth) Filtration Work?
- How Does Mesh (Surface) Filtration Work?
- Which Has Higher Dirt-Holding Capacity — Felt or Mesh?
- Can You Reuse a Mesh Filter Bag?
- What Micron Range Does Each Bag Type Cover?
- Which Type Should You Choose for Your Application?
- Where Do Oil-Sorbent (PSORB) Bags Fit In?
What's the Difference Between Felt and Mesh Filter Bags?
Felt bags filter by depth — the fibers are needled into a dense, three-dimensional mat, and particles get trapped throughout that thickness as fluid passes through. Mesh bags filter by surface — the fabric is a woven grid with a fixed opening size, and anything larger than that opening is stopped right at the surface. The distinction shows up directly in how each type is rated: felt bags carry a nominal micron rating (a typical, statistical capture efficiency at that size), while mesh bags carry an absolute micron rating (a hard cutoff — the pore size itself).
Why the Rating Type Matters
A nominal rating means some particles at or slightly above the stated size can still pass through some of the time — felt is a probability filter, not a sieve. An absolute rating means the bag is a physical sieve: nothing larger than the stated opening gets through, every pass. If your process has a hard spec — a downstream instrument that fouls above a certain particle size, or a QC pass/fail threshold — an absolute-rated mesh bag gives you that guarantee. If you're doing general pre-filtration or bulk solids removal ahead of a finer stage, a nominal-rated felt bag's higher capacity usually wins on cost per gallon treated.
How Does Felt (Depth) Filtration Work?
Felt filtration works by forcing fluid through a needled mat of fibers thick enough that particles get caught at multiple depths, not just at the entry surface — which is why felt bags hold significantly more contaminant before they clog or need changing. ERE stocks Sampson Platinum felt bags in two materials, both available from 1 to 200 microns with welded seams to prevent fiber migration into the process stream:
- Polypropylene felt bags — the most chemically inert felt media available, holding up against strong acids, alkalis, and aggressive solvents that degrade other materials. Common in chemical processing, petroleum, and groundwater remediation work.
- Polyester felt bags — resists most acids, organic solvents, and oxidizing agents, with better thermal stability at elevated process temperatures than polypropylene.
Both are disposable, single-use bags — once the depth of the media loads up with contaminant, differential pressure across the housing climbs and it's time for a changeout, not a cleaning.
How Does Mesh (Surface) Filtration Work?
Mesh filtration works by passing fluid through a woven fabric with a defined, uniform pore opening, so every particle above that size gets stopped at the surface in a single, predictable pass. ERE stocks two woven mesh constructions, both available with plastic or steel retainer rings:
- PEM (polyester multifilament) mesh bags — each strand is many smaller filaments twisted together, giving strong, economical woven filtration from 100 to 2,000 microns for coarser process water and wastewater pre-treatment.
- NMO (nylon monofilament) mesh bags — each filament is individually extruded to a consistent diameter, producing exact pore openings from 1 to 1,200 microns. The smooth monofilament surface resists particle embedding, which is why NMO bags can often be cleaned and reused across many applications — lowering cost per use versus a disposable felt bag.
Both constructions are silicone-free, which matters in automotive paint kitchens and mix rooms where silicone contamination ruins a finish.
Which Has Higher Dirt-Holding Capacity — Felt or Mesh?
Felt bags hold more contaminant before they need changing, because depth filtration uses the entire thickness of the media as storage, not just the surface. Mesh bags load up faster once the surface pores start blinding off — but that trade-off buys you the tighter, more repeatable cut point described above. In practice, many facilities run felt as a coarse pre-filter ahead of a fine mesh polishing stage, splitting the load between the two mechanisms rather than asking one bag to do both jobs.
Can You Reuse a Mesh Filter Bag?
Yes, in many applications — nylon monofilament (NMO) mesh bags have a smooth, non-porous filament surface that resists particles embedding into the media, so they can be rinsed clean and put back into service. Felt bags generally cannot be reused the same way, because particles that migrated into the depth of the media stay lodged there even after a rinse. If total cost of ownership over hundreds of change-outs matters more than the lowest per-bag price, NMO's reusability is the bigger lever than the micron rating itself.
A Safety Note on Spent Bags
Whichever type you run, a used filter bag carries whatever the process fluid carried — including any hazardous residue. Bags used in chemical service should be handled and disposed of per the material's WHMIS/GHS classification, not treated as ordinary shop waste.
What Micron Range Does Each Bag Type Cover?
Coverage varies by construction — felt runs a moderate range built for depth loading, while mesh spans from very fine (NMO) to very coarse (PEM):
| Bag Type | Filtration Mode | Rating Type | Micron Range | Reusable? |
|---|---|---|---|---|
| Polypropylene Felt | Depth | Nominal | 1–200 µm | No — disposable |
| Polyester Felt | Depth | Nominal | 1–200 µm | No — disposable |
| PEM Woven Mesh | Surface | Absolute | 100–2,000 µm | Limited |
| NMO Woven Mesh | Surface | Absolute | 1–1,200 µm | Yes, many applications |
All four are available in Sizes #1 through #4 to fit standard single- and multi-bag housings — see our full filter bag sizing and ring compatibility guide for exact dimensions, and our micron rating guide for how to pick the right cut point for your process.
Which Type Should You Choose for Your Application?
Choose felt when you need maximum dirt-holding capacity at the lowest cost per bag and don't need a hard particle-size guarantee. Choose mesh when your process needs a precise, repeatable cut point, or when reusability (NMO) matters more than the lowest unit price.
| If your priority is… | …choose |
|---|---|
| Maximum dirt capacity per changeout, lowest cost per bag | Felt (polypropylene or polyester) |
| Aggressive acid, alkali, or solvent chemistry | Polypropylene felt |
| Higher process temperature, oxidizing chemistry | Polyester felt |
| A hard, repeatable particle-size cutoff | Mesh (PEM or NMO) |
| Reusable, lower cost-per-use over many change-outs | NMO woven mesh |
| Coarse, high-volume pre-screening at low cost | PEM woven mesh |
Compare this against our polypropylene vs. nylon vs. polyester material guide for chemical compatibility, and our bag vs. cartridge filtration guide if you're weighing bag filters against a cartridge housing entirely.
Where Do Oil-Sorbent (PSORB) Bags Fit In?
Neither standard felt nor standard mesh is built to remove oil — for that, Sampson's PSORB filter bag uses an engineered core of shredded polypropylene microfiber inside an impermeable outer layer, forcing process fluid through the oil-adsorbing core instead of just past it. It's sized for 5–10 GPM flow rates to maximize contact time, and it targets non-emulsified oil specifically — a different removal mechanism than the particulate capture felt and mesh bags handle. Facilities discharging process water need to keep oil concentration under the receiving stream's limits; the CCME Canadian Water Quality Guidelines set the aquatic-life benchmarks most provincial discharge permits are built around, which is the regulatory driver behind adding an oil-sorbent stage like PSORB ahead of discharge.
For the full range of bag filter media ERE stocks, see the filter bags collection, or start with our complete filter bag selection guide if you're building out a filtration system from scratch.
Not sure whether felt or mesh is right for your process?
ERE Inc. has supplied industrial filtration equipment across Canada for 30+ years, distributing Sampson filter bags alongside housings, cartridges, and full liquid filtration systems. Tell us your fluid, flow rate, and target particle size and we'll spec the right bag.
→ Request a Quote | 1-888-287-EREC | Browse Filter Bags | sales@ereinc.com
Frequently Asked Questions
What's the difference between a nominal and an absolute micron rating?
A nominal rating (felt bags) means the media typically captures a stated percentage of particles at that size — some larger particles can still pass through occasionally. An absolute rating (mesh bags) means the media has a fixed, uniform pore opening that stops essentially all particles at or above that size, every pass.
Can mesh filter bags be reused?
Nylon monofilament (NMO) mesh bags can often be cleaned and reused in many applications because their smooth surface resists particle embedding. Felt bags are generally single-use, since particles lodge throughout the depth of the media and don't rinse out.
Which type has higher dirt-holding capacity, felt or mesh?
Felt holds more contaminant before it needs changing, because depth filtration uses the full thickness of the media rather than just the surface. Mesh bags load up faster but deliver a more precise, repeatable particle cutoff.
Do I need felt or mesh to remove oil from process water?
Neither — standard felt and mesh bags are built for solids, not oil. Sampson's PSORB bag uses an engineered oil-adsorbent core built specifically for non-emulsified oil removal at 5–10 GPM.
What sizes are Sampson felt and mesh filter bags available in?
Sizes #1 through #4, fitting standard single- and multi-bag housings, each available with a plastic or steel retainer ring. See our filter bag sizing and ring compatibility guide for exact dimensions per size.
Related articles
- Industrial Filter Bags: Complete Selection Guide for Canada 2026
- Polypropylene vs. Nylon vs. Polyester Filter Bags
- Filter Bag Micron Ratings: How to Choose the Right Filtration Level
- Bag vs. Cartridge Filtration: Which to Use
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