Air Filter Media Grades Explained: F5–F9 and ISO 16890

If you buy air filter media in rolls or finished pads, you have met the letter-and-number code: F5, F7, F9, and more recently ePM1 55% or ISO Coarse 65%. Suppliers often quote the old and new systems side by side without explaining them. Here is what they actually mean — and how to use them when specifying an order.

Where the grades come from

The F-grades (F5–F9) come from the European standard EN 779, which classified general ventilation filter media by how much of a synthetic dust they captured in a laboratory test. In 2019 EN 779 was withdrawn and replaced by ISO 16890, which grades filters by the share of particles they capture in three size bands:

ePM10 — particles up to 10 μm (coarse dust, pollen)
ePM2.5 — fine particles up to 2.5 μm (soot, smog)
ePM1 — the finest band, up to 1 μm (bacteria, combustion particles)

The percentage after ePM1 (say ePM1 55%) is the share of those particles the filter captures. "ISO Coarse" covers the heavy-dust pre-filtration classes.

The mapping table buyers actually need

Most mills — including ours — still quote both systems because legacy specifications live on in tender documents. This is the correspondence you will see in our typical grades table:

EN 779 Grade	ISO 16890 Equivalent	Typical Area Weight	Where It Is Used
F5	ISO Coarse 65%	≈ 280 g/m²	Pre-filtration, cabinet vents, machine intakes
F6	ePM10 50%	≈ 300 g/m²	General HVAC, office ventilation
F7	ePM1 55%	≈ 340 g/m²	Offices, schools, commercial buildings
F8	ePM1 70%	≈ 360 g/m²	Hospitals, electronics, food processing
F9	ePM1 80%	≈ 380 g/m²	Clean-room pre-filtration, labs, pharma

Values are typical industry figures; exact data sheets are supplied with every order.

Choosing a grade without overpaying

The most common specification error is jumping straight to F9 "for better air". Every step up the grade ladder costs more and loads the fan with more resistance — and if the fine media is not protected by a coarse pre-filter stage, it will clog in weeks. A well-designed system spends its budget like this:

F5 / ISO Coarse as the first stage — cheap, washable in many cases, takes the beating
F7 as the workhorse stage for most occupied spaces — this is the grade behind the majority of comfortable, compliant indoor air
F8–F9 only where the process demands it: hospitals, electronics, spray booths' final stage, food areas

For spray booths and paint shops, media choice also involves fiber type: synthetic media sheds paint mist without absorbing solvents, while fiberglass media (often with a scrim backing) is preferred for ceiling filtration where even airflow matters more than price.

What to confirm before ordering media in rolls

Grade and standard — insist both: "F7 / ePM1 55%" removes all ambiguity
Area weight (g/m²) — the honest indicator of dust-holding capacity
Initial pressure drop — determines your energy cost for the life of the filter
Roll width and length — standard widths up to 2.1 m; tell us your frame size and we suggest the most economical cutting layout
Fire performance — rail and transit work in particular requires media certified to standards such as DIN 5510-2

Bottom line

Specify by duty, not by habit. If your tender still says "F7" alone, quote it as F7 / ePM1 55% and you will get comparable offers from every serious supplier. If you are upgrading an old system, moving the final stage one grade up while protecting it with a proper F5 pre-filter usually delivers cleaner air at lower total cost than simply buying finer media everywhere.