Polypropylene vs Nylon vs Polyester Filter Bags | ERE

Every filter bag application starts with a material decision. Polypropylene, polyester, and nylon monofilament (NMO) each handle different chemistries, temperatures, and particle types — and choosing wrong means premature failure, contamination pass-through, or unnecessary cost. This guide is a companion to our Industrial Filter Bags: Complete Selection Guide and breaks down the three core materials head-to-head so you can match the right filter bag to your process conditions.

Filter Bag Material Comparison Table

All three materials are available in ERE's Sampson PLATINUM line in standard sizes #1 through #4. Here is how they compare on the specifications that matter for application selection:

When to Choose Polypropylene Felt Filter Bags

Polypropylene is the default material for industrial liquid filtration. If your process fluid is water-based, below 90 C, and does not involve aggressive solvents or strong oxidizers, polypropylene felt is almost certainly the right choice. It offers the broadest chemical compatibility of any common filter bag material across the full pH range (1 to 14), resists both mineral and organic acids, handles alkalis without degradation, and does it all at the lowest unit cost.

Typical polypropylene applications:

• Municipal and industrial water treatment
• Electroplating bath filtration
• Coolant and cutting fluid recycling
• Groundwater remediation pre-filtration
• Mild chemical process streams (aqueous acids, alkalis, brine)
• Pre-filtration ahead of cartridge or membrane systems

When to move away from polypropylene: If your process temperature exceeds 90 C, if you are filtering solvents (aromatics, chlorinated compounds, ketones), or if the stream contains strong oxidizers like nitric acid or chromic acid — polypropylene will soften, swell, or degrade. Switch to polyester or NMO depending on whether you need felt depth filtration or mesh precision.

When to Choose Polyester Felt Filter Bags

Polyester felt is the step-up material when polypropylene cannot handle the temperature or chemistry. With a maximum operating temperature of 150 C and strong resistance to organic solvents — including ketones, esters, and many aromatic compounds — polyester handles the process lines that polypropylene cannot survive.

Typical polyester applications:

• Paint, ink, and coating filtration
• Solvent recovery and reclamation
• Hot condensate return lines
• Aggressive chemical processing (organic solvents, oxidizing environments)
• Automotive electrocoat (e-coat) systems
• Pharmaceutical and cosmetics process lines with solvent contact

Polyester limitations: While polyester resists solvents that destroy polypropylene, it is weaker against strong mineral acids (sulfuric, hydrochloric at high concentrations) and concentrated caustic solutions above 100 C. For highly acidic streams, polypropylene remains the better felt option. Polyester is also disposable — if you need a reusable bag, NMO is the only option among these three materials.

When to Choose NMO (Nylon Monofilament) Filter Bags

NMO bags use a woven monofilament mesh instead of a felt matrix. Every opening in the weave is the same size, which gives NMO a sharp, absolute micron cut-point — particles above the rated size are captured, particles below pass through cleanly. This is fundamentally different from felt filtration, where particles are trapped at varying depths and the effective cut-point is nominal, not absolute.

The mesh structure also means NMO bags can be washed and reused. Contaminants collect on the surface rather than embedding in the fabric, so a cleaning cycle (pressure washing, ultrasonic bath, or chemical soak depending on the contaminant) restores filtration performance. Over multiple reuse cycles, the cost per use drops well below disposable felt bags.

Typical NMO applications:

• Food and beverage processing (food-grade, no fibre shedding)
• Resin and catalyst recovery
• Paint recirculation systems (precise particle classification)
• High-viscosity fluids (adhesives, polymers, syrups) where felt would blind immediately
• Any application requiring a known, repeatable particle cut-point
• High-change-frequency lines where reusability reduces operating cost

Sampson PLATINUM NMO bags are available from 1 to 1200 microns with double-stitched, silicone-free thread construction — critical for applications where silicone contamination is unacceptable (automotive paint lines, certain pharmaceutical processes).

NMO limitations: Nylon is attacked by mineral acids (hydrochloric, sulfuric, nitric) and has a narrower pH tolerance (3 to 11) than polypropylene. It also holds less total dirt per cycle than felt because filtration happens on the surface only. In high-solids-loading applications, NMO bags may need more frequent removal and cleaning even though they are reusable.

Chemical Compatibility Quick-Reference

This table covers the most common process chemicals encountered in Canadian industrial filtration. For chemicals not listed, contact ERE for a specific compatibility check.

Key pattern: Polypropylene handles acids and bases but fails with solvents and oxidizers. Polyester handles solvents and oxidizers but is weaker on strong mineral acids. NMO handles most organics but is vulnerable to any strong acid. When in doubt, polyester is the safest general-purpose upgrade from polypropylene.

Common Material Selection Mistakes

1. Running polypropylene above 90 C

Polypropylene begins to soften and deform above its rated temperature. In hot process lines, the felt loses structural integrity — the bag can collapse, bypass, or release trapped contaminants downstream. If your process runs hot even intermittently (steam cleaning cycles, batch heating), size for peak temperature, not average temperature. Above 90 C, switch to polyester or NMO.

2. Using felt where NMO precision is needed

Felt bags have a nominal micron rating — they capture most particles at the rated size but allow a percentage of same-size or larger particles through. For applications that require a hard cut-point (particle classification, product recovery, food-grade compliance), nominal filtration is not sufficient. NMO mesh provides an absolute rating: every opening is the same size, and nothing larger passes through.

3. Choosing NMO for high-acid streams

NMO is nylon. Nylon degrades in mineral acids — even dilute hydrochloric or sulfuric acid will attack the mesh over time, weakening the weave and eventually causing bag failure. If your process involves acidic streams and you need mesh-style filtration, consider stainless steel mesh bags or contact ERE for alternatives.

4. Ignoring solvent exposure on polypropylene

Polypropylene swells and softens in aromatic solvents, chlorinated solvents, and some esters. A bag that looks fine on initial installation can deform or fail within hours of solvent contact. Check every chemical in your process stream against polypropylene compatibility before defaulting to it.

5. Treating all felt bags as interchangeable

Polypropylene and polyester are both felt, but their chemical and thermal properties are significantly different. Substituting one for the other without checking compatibility can lead to premature bag failure. Always verify material compatibility for your specific process chemistry.

Frequently Asked Questions

What is the difference between felt and mesh filter bags?

Felt bags (polypropylene, polyester) use a non-woven fabric that traps particles throughout the depth of the material — giving high dirt-holding capacity but only a nominal micron rating. Mesh bags (NMO) use a woven monofilament structure with uniform openings for an absolute micron cut-point and can be washed and reused, but hold less total contaminant per cycle.

Can I use a polypropylene filter bag with solvents?

No. Polypropylene swells and degrades in aromatic solvents, chlorinated solvents, ketones, and esters. For solvent-contact applications, use polyester felt bags, which resist most organic solvents including acetone, MEK, toluene, and ethyl acetate.

How many times can NMO filter bags be reused?

NMO bags can typically be cleaned and reused 5 to 20+ times depending on the application, contaminant type, and cleaning method. Contaminants that sit on the mesh surface (particulates, crystals) wash off easily. Sticky or biological contaminants may require more aggressive cleaning and reduce the total number of reuse cycles.

Which filter bag material is best for food processing?

NMO (nylon monofilament) is the standard choice for food and beverage filtration. The woven mesh does not shed fibres into the process stream, provides an absolute micron cut-point for consistent product quality, and can be cleaned to food-safety standards between batches. Sampson PLATINUM NMO bags use silicone-free thread, which is required in many food processing specifications.

Related articles

• Industrial Filter Bags: Complete Selection Guide
• Bag Filter Housings: Sizing & Selection Guide
• Filter Bag Sizes: Dimensions, Rings & Compatibility
• Multi-Bag vs. Single-Bag vs. Duplex Filter Housings
• Filter Bag Micron Ratings: How to Choose

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