Ceiling Tiles: How to Read NRC, CAC, Fire Class and Material

By Miguel Duarte · 10 September 2026

Ceiling tiles look interchangeable in a showroom. They are not, and the differences are not visible from the floor.

Two panels can share a size, a colour and a price. One will quieten the room and leak speech next door. The other does exactly the reverse of that.

The difference sits on the datasheet, not on the face.

What Ceiling Tiles Are Rated For

One standard sets what the datasheet has to tell you.

The Four Numbers That Matter

ASTM E1264 classifies acoustical ceilings three ways. It sorts them by type, by pattern and by rating. The ratings cover sound, light reflectance and fire.

• NRC says how much sound the panel absorbs inside the room itself. - Measured in a single room with no partition involved.
• CAC says how much sound the panel blocks on its way to the next room. - Measured across a plenum shared by two rooms on either side.
• Fire class says how far flame spreads across the face of the panel.
• Light reflectance says how much of the lighting design the ceiling gives back.

Absorption and Blocking Are Different Jobs

Absorption cuts noise in the room you stand in. Blocking stops noise crossing a partition. Most ceiling tiles are good at one, not both.

A soft, open panel absorbs well. A dense, sealed panel blocks well.

What the Standard Leaves Out

ASTM E1264 excludes physical properties on purpose. Sag, friability, hardness, linear expansion and transverse strength all sit outside its scope.

Those properties decide whether ceiling tiles survive a humid plenum. They have to be checked on the maker's own data.

NRC: How Much Sound Ceiling Tiles Absorb

Absorption is the rating most buyers of ceiling tiles already know.

How NRC Is Measured

The Noise Reduction Coefficient comes from ASTM C423. The test runs in a reverberation room with almost no absorption of its own. Four octave bands are averaged: 250, 500, 1000 and 2000 Hz.

The average is rounded to the nearest multiple of five hundredths. A wider average, the Sound Absorption Average, is slowly replacing it.

The Numbers to Specify

New York State sets a floor for public buildings. It is a fair private benchmark too.

Panels should absorb about two thirds of the sound reaching them. In open plan space that rises to roughly three quarters.

Space type	Minimum NRC	Minimum CAC	Why
Open plan office	0.75	35	Speech has to die where it starts
Closed office or classroom	0.65	35	Absorption plus a barrier over the partition
Space with noisy plenum kit	0.65	35	Fans and ducts sit right above the panel
Standard mineral fibre, 3/4 in	0.65 to 0.75	35 to 39	The commodity panel covers both cases

• Open plan space needs the highest absorption of any ceiling tiles on the list.
• Closed rooms can drop one step down the absorption scale without complaint.
• Noisy plenums raise the barrier target rather than the absorption target.

CAC: How Much Sound Ceiling Tiles Block

Blocking is the rating people forget until a meeting is overheard.

How CAC Is Measured

Ceiling Attenuation Class comes from ASTM E1414. In the test two rooms share one continuous ceiling plenum. A source sits above the ceiling on one side and a microphone below it on the other.

The result grades the ceiling as a barrier rather than a sponge.

When CAC Beats NRC

A partition that stops at the ceiling line hands its job upward. That is how most offices, clinics and classrooms are built.

• Partitions run to the slab make the barrier rating far less critical.
• Partitions run to the ceiling line make the ceiling tiles the whole defence. - High absorption with a low barrier rating still leaks speech next door.
• Noisy plenums need a barrier rating whatever the partitions below them do.
• Confidential rooms are specified on the barrier rating first and absorption second.

Fire Class

Fire performance is a pass or fail gate rather than a preference.

Class A, B and C

Surface burning is tested to ASTM E84. It reports a flame spread index and a smoke developed index.

Class	Flame spread index
Class A	0 to 25
Class B	26 to 75
Class C	76 to 200

Commercial ceiling tiles are normally specified as Class A. The New York specification requires it for standard mineral fibre panels.

Smoke Developed

Flame spread is only half the result. For vinyl-wrapped ceiling tiles the same specification caps smoke developed at 50. Flame spread on the same panel must not exceed 25.

Perlite panels are the outlier. They are specified at zero flame spread and zero smoke development.

Ceiling Tile Materials

Material follows the ratings, the room and the cleaning regime.

Material	Strengths	Watch for
Wet-pressed mineral fibre	Commodity price, balanced ratings, high recycled content	Starch and biocides, moisture
Fibreglass	Strong absorption, recycled content up to 90 percent	Binder chemistry, facing wear
Non-wet-formed perlite	Zero flame spread, no food for microbes	Lower absorption and light reflectance
Metal	Very high recycled content, washable, long life	Needs an acoustic backing
Wood or agri-based	Warm look, renewable content	Emissions rating, moisture

Mineral Fibre

Wet-pressed mineral fibre is the standard commercial panel. It is made from waste paper, mineral fibre and cornstarch. The mineral fibre may include slag from steelmaking.

• Recycled content is often 75 percent or more of pre-consumer material.
• Formaldehyde is present at low levels in some of these products.
• Starch and biocides raise a mould question in plenums that stay damp. - Mineralised wood-fibre panels belong nowhere near an area exposed to moisture.
• Ratings sit in the middle of the scale for both absorption and blocking.

Fibreglass

Fibreglass ceiling tiles absorb strongly and are faced with a cloth, fibreglass or vinyl scrim. Recycled content can reach 90 percent.

Most use a phenol-formaldehyde binder. Formaldehyde-free binders are specified where air quality is certified.

Perlite

Non-wet-formed perlite is made from expanded volcanic perlite, ceramic clay and inorganic binders. The panels are fireproof and will not feed microbial growth.

The trade-off is acoustic and visual. Light reflectance and absorption are both lower than mineral fibre.

Metal and Timber

Metal ceiling tiles carry high recycled content and wash down well. On their own metal ceiling tiles absorb almost nothing at all. An acoustic backing is part of the specification rather than an optional upgrade.

Wood and agri-based panels bring a warmer finish. Fibreboard panels should meet the relevant emissions standard.

• Metal ceiling tiles suit wash-down rooms and a long service life.
• Timber panels suit front of house areas, atria and reception spaces.
• Both need the acoustic layer written into the specification separately.

Sizes, Fit and Wet Areas

A correct rating is wasted if the panel does not sit down.

The Two Standard Sizes

Almost all suspended grid work runs on two modules. The first is 24 by 24 inches, usually written as 2 feet square. The second module is 24 by 48 inches.

Metric markets sell these as 600 by 600 mm and 1200 by 600 mm.

A third common size, 12 by 12 inches, is sold for direct-fix residential ceilings rather than for a grid.

Nominal Versus Actual

Metric ceiling tiles are cut slightly under the nominal figure. Distributor data puts the actual sizes at 595 by 595 mm and 1195 by 595 mm.

Cut a panel to the nominal dimension and it will not drop in.

• Start from the room use, because it sets both acoustic targets.
• Set the absorption target before looking at a single product page.
• Set the barrier target from the height at which the partitions stop.
• Confirm the fire class that the occupancy and the local code demand.
• Match the material to the cleaning regime and the humidity of the plenum.

Humid and Wet Areas

Wet rooms need ceiling tiles rated for the condition. The New York specification calls for RH-90 humidity performance.

• Kitchens usually land on vinyl-wrapped or metal ceiling tiles for washability.
• Wash-down areas need a face that survives a hose and a detergent.
• Clinical rooms need cleanability and a fire class at the same time.

Browse ceiling tiles and panels for the panels, ceiling tile grids for the suspension system, and ceiling tile tools and hardware for the cutting and fixing kit.

Frequently Asked Questions

What is the difference between NRC and CAC on ceiling tiles?

NRC measures how much sound the panel absorbs in a room, tested to ASTM C423. CAC measures how much it blocks between two rooms sharing a plenum, tested to ASTM E1414.

What NRC should an open plan office specify?

Roughly three quarters of the sound reaching the panel should be absorbed. A closed office or classroom can drop to about two thirds.

Are all commercial ceiling tiles Class A?

Not automatically, although most commercial specifications for ceiling tiles require it.

What size are standard ceiling tiles?

Two modules cover almost all suspended grid work: 24 by 24 inches and 24 by 48 inches. Metric equivalents sell as 600 by 600 mm and 1200 by 600 mm, cut marginally undersize so they drop into the grid.

Which ceiling tiles suit a kitchen or wash-down area?

Panels rated for high humidity, which usually means vinyl-wrapped, metal or perlite. Ordinary mineral fibre and mineralised wood-fibre panels should stay out of damp rooms.

Conclusion

Ceiling tiles are a four-number purchase dressed as a finish. Absorption, blocking, fire class and light reflectance decide the outcome. The face pattern decides almost nothing.

The order of the decisions matters as much as the numbers.

Fix the acoustic targets from the room and the partitions. Take the fire class from the occupancy, then pick a material that survives the plenum.

• Absorption and blocking trade against each other in almost every panel.
• Fire class is a gate, and smoke is part of it.
• The classification standard says nothing about sag, handling or long-term strength.
• Moisture rules out more ceiling tiles on site than any other condition.