+86 180 1863 2298 service@pulomax.com
Choosing a ceiling means reading two numbers: NRC and CAC. They are not the same thing. NRC (Noise Reduction Coefficient) measures how much sound a ceiling absorbs inside a room. CAC (Ceiling Attenuation Class) measures how well that ceiling blocks sound traveling to the next room. This guide to NRC vs CAC explains the difference in plain English, with a comparison table and a short checklist you can use right away.
Many buyers think a "better" ceiling just means higher numbers. That is wrong. A ceiling can score high on one number and low on the other at the same time, so pick the number that fits your room.
The two numbers sit on the same label, which is exactly why specifiers mix them up. Maxing out one does nothing for the other.
NRC (Noise Reduction Coefficient) is a score from 0 to 1. It shows how much echo and reverberation a ceiling removes from the room you are standing in. A high NRC means speech is clearer and the room feels calm. A bare concrete or glass ceiling reflects almost all sound, so its NRC is near zero. Most good commercial ceilings land between 0.50 and 0.90. NRC is measured in a lab per ASTM C423.
CAC (Ceiling Attenuation Class) is a single number, usually from 25 to 45. It shows how much sound leaks to the room next door through the plenum. A high CAC means better privacy between rooms. CAC is a system rating, not a single tile rating, which is why installation matters so much. It is measured per ASTM E1414 and E1111.
NRC is about the room you are in. CAC is about the room next door. One controls echo. The other controls privacy.
| Dimension | NRC (Noise Reduction Coefficient) | CAC (Ceiling Attenuation Class) |
|---|---|---|
| What it measures | In-room sound absorption (echo, reverberation) | Room-to-room sound isolation through the plenum |
| Typical range | 0.50 – 0.90 (higher with engineered systems) | 25 – 45; 35+ is high privacy |
| A high value means | Quieter room, clearer speech inside | Stronger privacy, neighbors hear less |
| Best for | Open offices, classrooms, restaurants | Exam rooms, boardrooms, hotels, legal suites |
The one sentence to remember: a ceiling with high NRC can still have low CAC, and the other way around. The two numbers answer different questions, so a strong score on one will not rescue the other.
The most common error is buying for NRC and forgetting CAC. A clinic can have a quiet room that still leaks talk to the next room. For any space where privacy matters, check both numbers — not just the one on the brochure.
Start with the problem your room actually has, then set a target before you look at products. Match the rating to the failure mode you want to avoid, not to a generic "good ceiling" idea.
Echo problem? Raise NRC. Open offices and classrooms need NRC 0.70 or higher for clear speech.
Privacy problem? Raise CAC. Exam rooms and boardrooms need CAC 35 or higher for real privacy.
Both problems? Set both targets on the spec sheet before comparing products.
Want a metal look? Use a perforated metal or aluminum system with acoustic backing to reach both ratings.
Use this quick target guide by room type.
Open office / co-working — NRC 0.70+, CAC 25–33 (layout gives privacy)
Classroom / lecture hall — NRC 0.70+, CAC 30+
Medical exam room / clinic — NRC 0.60–0.75, CAC 35+
Boardroom / legal suite — NRC 0.65–0.80, CAC 35–40
Hotel room / corridor — NRC 0.55–0.70, CAC 35+
Material is the lever that moves both numbers. Our mineral fiber ceiling tiles deliver balanced NRC (0.55–0.85) and CAC (34–37) at a low cost, which suits most offices, schools, and clinics.
For design-led spaces, our acoustic honeycomb ceiling panels reach NRC up to 0.85 with the right backing. Metal alone reflects sound; the acoustic work happens behind the face with backing or infill.
All our ceilings carry fire ratings too. Mineral fiber meets ASTM E84 Class A. Aluminum honeycomb meets EN 13501-1 A2. You can meet acoustic and fire rules in one submittal.
CAC is won or lost in the field, not the factory. Even a strong tile underperforms if sound slips through the plenum. Seal the tops of partitions, and treat every light fixture, diffuser, and sprinkler that cuts through the ceiling.
NRC (Noise Reduction Coefficient) is a 0-to-1 rating of how much sound a ceiling absorbs inside a room. Higher NRC means less echo and clearer speech in that room. It is measured per ASTM C423 on the product's real mounting.
CAC (Ceiling Attenuation Class) is a single-number rating of how well a ceiling blocks sound traveling to the next room through the plenum. Higher CAC means better speech privacy with the room next door. It is measured per ASTM E1414 and E1111 on a full ceiling assembly.
No. A very high NRC cuts echo but does nothing for privacy. In exam rooms or boardrooms, you also need high CAC for confidentiality. Choose the NRC your space type actually requires, not the highest number on the shelf.
Bare metal reflects sound and performs poorly on its own. But a perforated metal or aluminum ceiling tiles and planks assembly — with acoustic backing, infill, or a sealed plenum — can reach NRC up to 0.85 and CAC 35+.
Classrooms need NRC 0.70 or higher for speech clarity, with CAC 30+ where rooms sit next to each other. Exam rooms and boardrooms need CAC 35+ for privacy. See our acoustic ceiling FAQ for more detail on sealing and plenum work.
Still unsure which number your project needs? PuloMax is a manufacturer with its own factory, not a trading reseller, so we can match a rating to your budget and look. We ship to more than 20 countries and regions.
Send us your room type and we will suggest a panel. Learn more about PuloMax, or Request a quote for NRC, CAC, and fire test data matched to your standard (ASTM or EN).