Mesh to Micron Conversion: The Complete Guide for Plastic Extrusion
Mesh count and micron opening are not the same number — and confusing them costs extrusion lines real money. A 200-mesh woven wire screen opens at 74 microns. Switch to a metal nonwoven screen and you can reach 3 microns with no equivalent mesh number at all. This guide gives process engineers and plant managers a reliable mesh-to-micron reference, explains the underlying engineering, and maps filtration fineness to extrusion applications.
What mesh count actually means
Mesh count is the number of wires per linear inch in a woven wire screen — nothing more. A 100-mesh screen has 100 wires per inch in each direction, forming a grid. The actual opening between those wires depends on the wire diameter, which is a separate variable.
ASTM E11 and ISO 3310-1 define standard relationships between mesh count, wire diameter, and nominal opening size for woven wire cloth. These standards are the authoritative source for the conversions used throughout this guide. Two screens with identical mesh counts but different wire diameters will have different micron openings — a critical point that single-column conversion charts often ignore.
For plastic extrusion, the practical consequence is straightforward: specifying only a mesh count without referencing the wire diameter leaves filtration fineness undefined. Always confirm the nominal opening in microns when ordering screen packs.
Why mesh and microns are not the same number
The opening size (in microns) of a woven wire screen is calculated as: opening = (25,400 / mesh count) − wire diameter (both in µm). For a standard 200-mesh screen with a wire diameter of approximately 53 µm, the nominal opening works out to 74 µm. Change the wire diameter to 63 µm and the same mesh count gives only 64 µm.
This is why the Dynisco Extrusion Handbook — one of the industry’s standard references — states that mesh count alone is insufficient to specify filtration: the wire diameter must accompany it. In practice, most screen suppliers use a de-facto standard wire diameter for each mesh count, which is what the conversion table below reflects.
Metal nonwoven screens (sintered fibre mats) break the formula entirely. They have no wires, no mesh count, and no calculable opening. Their filtration rating is expressed exclusively in microns, derived from bubble-point testing per ISO 4003. For fine filtration below 20 µm in extrusion, nonwovens are the only practical option.
Standard mesh-to-micron conversion table
The table below covers the mesh counts most commonly used in plastic extrusion screen changers, from coarse contamination removal to fine gel filtration. Values reflect standard wire diameters per ASTM E11 / ISO 3310-1.
| Mesh count | Nominal opening (µm) | Wire diameter (µm) | Typical extrusion applications |
|---|---|---|---|
| 20 | 841 µm | 380 µm | Coarse pre-filtration, recycling lines |
| 40 | 400 µm | 235 µm | Compounding, pipe extrusion |
| 80 | 177 µm | 140 µm | Cast film, sheet extrusion, blow moulding |
| 100 | 149 µm | 110 µm | Wire & cable insulation, extrusion coating |
| 200 | 74 µm | 53 µm | Blown film (PE/PP), BOPP, BOPET |
| 325 | 44 µm | 35 µm | Stretch film, fiber spinning, premium film |
| — (nonwoven) | 10 µm | N/A (sintered fibre) | Fine film, fiber spinning · AP Series |
| — (nonwoven) | 3 µm | N/A (sintered fibre) | Gel removal, premium optical film · AP Series finest |
For instant conversion of any mesh count — including intermediate values not shown above — use the Cofit Mesh-to-Micron Interactive Calculator. It handles both woven wire and metal nonwoven screen types and maps the result to the corresponding AP Series filtration spec.
When woven wire is not enough: metal nonwoven screens
At 325 mesh (44 µm), woven wire screens approach their practical limit for extrusion. Finer weaves — 400 or 500 mesh — are technically possible but fragile, prone to blinding, and generate back pressure that most screen changers cannot sustain without excessive pressure drop.
Metal nonwoven screens solve this by using a sintered mat of randomly oriented metal fibres. Their structure creates a tortuous flow path that captures particles far smaller than the nominal pore size, achieving ratings of 3–20 µm at manageable differential pressure — provided the screen changer has sufficient filtering area.
This is the critical constraint. Standard piston screen changers lack the filtering area to run nonwoven screens without excessive back pressure. The Cofit AP Series is designed with a large filtering area specifically to accommodate metal nonwoven media, enabling gel removal down to 3 µm — a spec relevant for optical film, fine fiber, and food-contact applications where fish-eye defects are a quality reject criterion.
How filtration fineness affects your extrusion process
Choosing a finer screen removes more contamination — but it also increases differential pressure (ΔP) across the screen pack and accelerates clogging. The trade-off has direct production consequences: faster clogging means more frequent screen changes, and on lines with standard screen changers, each manual change means 15 to 45 minutes of production stop.
At a typical extrusion line downtime cost of $200–$500 per hour (Plastics Technology benchmark), a single extra screen change per shift adds $50–$375 in lost production daily. Across a year, that compounds into a measurable OEE (Overall Equipment Effectiveness) gap — industry data shows a 5–15% OEE improvement when moving from manual to continuous screen changers on lines with frequent change intervals.
“The question is never just which micron rating you need — it’s whether your screen changer can maintain that rating continuously without turning screen changes into a downtime event.”
— Process Engineer, film extrusion line, Northern Europe
Melt pressure stability is the second variable. Continuous screen changers — including the Cofit AP Series — maintain melt pressure within ±2% during screen changes, preventing the pressure spikes that cause gauge variation in film and wall thickness irregularities in pipe. Standard screen changers interrupt flow, causing transient pressure drops that show up as rejects at the winder or downstream inspection.
What is your screen change really costing you?
Enter your throughput, stop frequency, and shift schedule in Cofit’s free Productivity Savings Calculator to see exactly how many kilograms — and how much revenue — you lose to screen change downtime each month.
Choosing the right screen for your application
Filtration fineness selection depends on three factors: the contamination level of your feedstock, the quality requirements of your product, and the back pressure your extruder can sustain.
| Application | Recommended fineness | Screen type | Key driver |
|---|---|---|---|
| Post-consumer recycling | 150–400 µm | Woven wire (coarse) | High contamination, throughput priority |
| Pipe & blow moulding | 100–200 µm | Woven wire (medium) | Wall integrity, long-term pressure |
| Wire & cable | 74–149 µm | Woven wire (fine) | Insulation dielectric quality |
| Blown film / BOPP | 44–74 µm | Woven wire (fine) | Optical clarity, gel removal |
| Fiber spinning / stretch film | 10–44 µm | Woven wire or nonwoven | Spinneret life, consistency |
| Premium optical film | 3–10 µm | Metal nonwoven only | Zero fish-eye tolerance |
For the finest filtration ranges (3–10 µm), the screen changer must provide enough filtering area to prevent excessive back pressure. Standard piston designs typically cannot. The Cofit AP Series — with its enlarged filtering cavity — is specifically engineered to support metal nonwoven screens without compromising melt pressure stability. See the full specification at cofit.com/ap-screen-changer.
Common misconceptions about mesh and micron in extrusion
Myth
A higher mesh number always means finer filtration.
Reality
Only if wire diameter is held constant. A 200-mesh screen with a heavy wire is coarser than a 200-mesh screen with a fine wire.
Myth
You can always convert microns to mesh using a simple formula.
Reality
The formula requires wire diameter as an input. Without it, any single-column mesh/micron chart is an approximation based on assumed wire diameters.
Myth
Finer screen = better product quality, always.
Reality
Finer screens increase back pressure and change frequency. Without a continuous screen changer, finer filtration can increase downtime and reduce net OEE.
Frequently asked questions
A standard 200-mesh woven wire screen (ASTM E11 / ISO 3310-1 specification) has a nominal opening of 74 microns. This assumes a standard wire diameter of approximately 53 µm. If a supplier uses a heavier wire, the opening will be smaller; a lighter wire gives a larger opening. Always confirm the nominal opening in µm when ordering.
A 325-mesh woven wire screen opens at approximately 44 microns with a standard wire diameter of 35 µm. This is near the practical limit for woven wire in extrusion — finer weaves become mechanically fragile and generate excessive back pressure in most screen changers.
With metal nonwoven screens on a screen changer designed with sufficient filtering area — such as the Cofit AP Series — filtration down to 3 microns is achievable without excessive back pressure. Woven wire screens typically reach 44 µm (325 mesh) as a practical minimum in continuous operation.
Most blown film lines for PE and PP use 200-mesh (74 µm) or 325-mesh (44 µm) screens. BOPP and BOPET lines often require finer filtration — down to 44 µm or below — to meet optical clarity and gel count specifications. The exact selection depends on resin quality, line speed, and customer quality requirements. Use the Cofit Mesh-to-Micron Calculator to map your target micron rating to the correct mesh count.
Yes — in practice. A continuous screen changer maintains stable differential pressure because screens are replaced without stopping the line. This allows finer screens to be used at steady state without the pressure spikes and downtime that make fine filtration impractical on manual screen changers. The Cofit AP Series can sustain 3-micron nonwoven screens in continuous operation on demanding film and fiber lines.
Find the right filtration spec for your line
Use the interactive calculator to convert any mesh count to microns and see the matching AP Series filtration spec. Then run the Productivity Savings Calculator to quantify what your current screen change interval is costing you.
Sources and references
- ASTM E11 — Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves, ASTM International
- ISO 3310-1 — Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth, International Organization for Standardization
- ISO 4003 — Permeable sintered metal materials — Determination of bubble test pore size, International Organization for Standardization
- Giles, H.F., Wagner, J.R., Mount, E.M. — Extrusion: The Definitive Processing Guide and Handbook (Dynisco / William Andrew Publishing)
- Cofit International — AP Series technical specifications, cofit.com/ap-screen-changer/
- Plastics Technology — Extrusion line downtime cost benchmarks, ptonline.com
Cofit deals with research, engineering, manufacture and distribution of automatic and continuous screen changers for post-consumer and post-industrial recycling materials too.
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