Buying the right paint booth filter is a lot easier when you speak the language. Spec sheets, compliance rules, and vendor catalogs are full of shorthand — arrestance, MERV, ePM, F5/M5, plenum, tackified, w.c. — and getting one term wrong can mean the wrong media in your booth, a failed inspection, or a finish full of dirt nibs. This glossary defines the 30 terms that matter most, grouped so you can find them fast, with links to deeper how-to guides when you want the full story.
Use it as a reference: skim the table for a quick definition, then follow the links for the terms you need to act on. If you're brand new to booth filtration, start with our overview of how spray booth filters work, then come back here to nail down the vocabulary.
The 30 terms at a glance
Here's the fast-reference table. Definitions below the table add context where a one-liner isn't enough.
| Term | What it means |
|---|---|
| Arrestance | A weight-based rating of how much test dust a filter captures, by weight. The right yardstick for overspray, which is heavy and coarse. |
| MERV | Minimum Efficiency Reporting Value (1–16), from ASHRAE 52.2. A particle-size-based efficiency scale, not a weight measure. |
| F5 / M5 | Ceiling/intake media efficiency classes from the older EN 779 standard. Typical of paint-booth ceiling filters that give a clean supply air stream. |
| ISO 16890 / ePM | The current international filter standard. Efficiency is reported as ePM1, ePM2.5, or ePM10 — the percentage of that particle size a filter removes. |
| Downdraft | Booth design where clean air enters through the ceiling and exhausts down through a floor pit. Best finish quality. |
| Crossflow | Air enters at one end wall and exits the opposite end. The most economical layout. |
| Semi-downdraft | Hybrid: air enters the front ceiling and exhausts through the rear lower wall. |
| Plenum | The chamber above the ceiling filters (or behind the exhaust filters) that distributes or collects air evenly. |
| Tackified | Media coated with a tacky adhesive so captured particles stick and don't blow back into the airstream. |
| Accordion filter | Folded kraft-paper exhaust filter (Andreae-style) whose zig-zag shape adds surface area and holding capacity. |
| Pocket / bag filter | Deep, extended-surface exhaust filter used as a final stage for high dust-holding capacity. |
| Prefinal / staging | Multi-stage exhaust setup where a first stage catches bulk overspray and protects a higher-efficiency final stage. |
| Manometer | A gauge that reads the pressure difference across your filters so you know when they're loaded. |
| Magnehelic | A popular brand of diaphragm dial gauge used as a booth manometer. |
| Water column (w.c.) | The pressure unit booths use — inches of water column. Filter change points are given in inches w.c. |
| NESHAP 6H | The federal area-source air rule (40 CFR 63 Subpart HHHHHH) that requires qualifying exhaust filters for most paint shops. |
| NFPA 33 | The fire-safety standard for spray application — governs booth construction, airflow velocity, and fire protection. |
| Dirt nib | A small raised bump in a cured finish caused by a trapped particle. The enemy of a show-quality coat. |
| Overspray | Atomized paint that misses the part and travels into the exhaust air — what your exhaust filters are there to catch. |
| Intake / ceiling filter | Media at the air supply that gives incoming air a final clean before it reaches the part. |
| Exhaust filter | Media on the exhaust side that captures overspray before air leaves the booth. |
| Prefilter | A coarse first-stage filter that protects a finer downstream filter or the air makeup unit. |
| Panel filter | A rigid, framed filter panel — pleated or link-style — that drops into a track or frame. |
| Pleated filter | Media folded into pleats to pack more surface area into the same face size. |
| Roll media | Bulk filter material on a roll, cut to length for ceiling grids or exhaust frames. |
| Fiberglass filter | Spun-glass exhaust media, often progressively dense and tackified, used as an economical overspray filter. |
| Polyester media | Synthetic, progressively structured media with more loft and higher dust-holding than fiberglass. |
| Face velocity | The speed of air moving through the booth cross-section, in feet per minute (fpm). |
| Static pressure / ΔP | Resistance to airflow across the filters. It rises as filters load — the signal to change them. |
| Dust-holding capacity | How much particulate a filter can hold before it reaches its final rated resistance. |
| Air makeup unit (AMU) | The unit that heats, conditions, and supplies replacement air to keep the booth balanced. |
Rating and efficiency terms
Arrestance vs. MERV — don't mix them up
This is the single most confused pair in booth filtration. Arrestance is a weight-based measure: challenge a filter with a known mass of test dust, weigh what it caught, and report the percentage. Because overspray particles are large and heavy, weight-based arrestance is the correct way to describe an exhaust filter's overspray efficiency. MERV, on the other hand, is particle-size-based — it scores how well a filter captures particles across size ranges from 0.3 to 10 microns. A high MERV number tells you about fine-particle performance; it does not tell you the weight-based overspray capture your compliance rule cares about. We break the difference down in detail on our MERV vs. arrestance and the 98% rule page and in the companion article on the 98% capture rule explained.
F5/M5 and ISO 16890/ePM
F5 and M5 are efficiency classes from the older European EN 779 standard, commonly quoted for ceiling and intake media — the kind that gives you a clean supply airstream over the part. The current standard, ISO 16890, reports efficiency as ePM1, ePM2.5, or ePM10 — the percentage of particulate of that size the media removes. When a data sheet lists both, use them to compare like with like across brands rather than trusting marketing adjectives like "premium" or "high-efficiency."
Booth design and airflow terms
Your booth's airflow pattern decides which filters you need and where. Downdraft booths pull clean air from a full ceiling of intake filters straight down over the part and out through a floor pit — the cleanest possible path, favored for show and OEM-quality work. Crossflow booths move air end to end and are the most economical. Semi-downdraft splits the difference. The plenum is the chamber that spreads incoming air evenly across the ceiling filters (or collects exhaust behind the wall filters); an unbalanced plenum shows up as uneven filter loading. For a full comparison, see our sibling guide on downdraft, crossflow, and semi-downdraft filtration and the fundamentals in the direction of airflow in paint booths.
Face velocity — the speed of air through the booth cross-section in fpm — is what fire and air rules reference for capture and safe operation, and it drops as your filters load. The air makeup unit (AMU) conditions and delivers the replacement air that keeps velocity and booth pressure where they belong.
Media and construction terms
On the intake side you'll meet panel, pleated, and roll forms of ceiling media, plus coarse prefilters that protect them. On the exhaust side, fiberglass and polyester media, the folded accordion filter, and deep pocket/bag filters each trade cost against holding capacity. If the intake-side vs. exhaust-side split still trips you up, our primer on intake filters vs. exhaust filters sorts out which media does which job. Tackified media is coated to grab and keep overspray so it doesn't re-enter the airstream — important on final stages; our comparison of tackified vs. non-tackified ceiling media covers when each is the right call. Many booths run a prefinal/staging arrangement, letting a cheaper first stage take the brunt so the final filter lasts longer. Browse the full range in all paint booth filters, or jump to ceiling and intake filters and exhaust filters.
Measurement and compliance terms
Manometer, Magnehelic, and water column
Your manometer reads the pressure difference across the filters; a Magnehelic is a common dial-gauge version. Readings are in inches of water column (w.c.). When the gauge climbs to your filter's rated final resistance, it's time to change — that's the whole point of measuring rather than guessing. Learn to read yours with our guide to reading a paint booth manometer.
NESHAP 6H and NFPA 33
NESHAP 6H — the federal area-source air rule at 40 CFR 63 Subpart HHHHHH — requires that most paint shops use exhaust filter technology demonstrated to capture at least 98% of paint overspray, measured by weight (40 CFR 63.11173(e)(2)(i)). Note the wording: it is a weight-based capture requirement, not "98% at 3 microns" — that phrase is vendor shorthand, not the rule. NFPA 33 is the separate fire-safety standard that governs booth construction, airflow velocity, and fire protection. The two work together: 6H covers emissions, NFPA 33 covers fire and airflow. Our compliance deep-dive and the compliance hub keep the certificates and details in one place. This is general information, not legal advice — confirm requirements with your state or local air authority.
Frequently asked questions
What's the difference between arrestance and MERV?
Arrestance is weight-based — the percentage of a dust challenge captured by weight — and is the right measure for coarse, heavy overspray. MERV is particle-size-based and describes fine-particle efficiency. For exhaust/overspray filters, arrestance and the weight-based 98% capture figure are what matter for compliance.
Does the NESHAP 6H rule really mean "98% at 3 microns"?
No. The rule requires exhaust filtration demonstrated to capture at least 98% of paint overspray measured by weight, per 40 CFR 63.11173(e)(2)(i). "98% at 3 microns" is a marketing paraphrase, not the regulatory text. Always confirm specifics with your air authority.
What is a plenum and why does it matter?
The plenum is the chamber that distributes supply air across the ceiling filters or collects exhaust behind the wall filters. A well-balanced plenum loads filters evenly; an unbalanced one causes hot spots, uneven loading, and inconsistent airflow over the part.
What does "tackified" media do?
Tackified media carries an adhesive coating so captured particles stick in place and don't blow back into the airstream. It's used where re-entrainment would hurt — final exhaust stages and quality-critical ceiling media.
How do I know which of these filters my booth needs?
Identify your booth's airflow type and stages, then match media by stage. Our Find My Filter tool and team can size it with you. When in doubt, measure your existing filters and match by type and size rather than chasing a part number.
Speak the language, buy with confidence
Once these 30 terms click, spec sheets stop being intimidating and you can buy exactly what your booth needs — no guesswork, no wrong media. Ready to put it to use? Browse our full paint booth filter catalog, or reach out through Find My Filter and we'll match the right filters to your booth, stage by stage.