When selecting an acoustic panel, the first question is always "which thickness should I choose?" Thickness is not a simple specification — it determines which frequencies are absorbed and how quiet the space can become. This article explains the actual role each thickness plays, using the internationally recognised room acoustics standard DIN 18041 (German Indoor Acoustics Standard) as the reference framework.
PET NRC by thickness (KCL certified)
◆ = best in class. NRC ≥ 0.75 qualifies as excellent absorption.
Tornex PET acoustic panels are offered in three KCL-certified thicknesses. An NRC of 0.75 or above is classified as "excellent absorption." However, the real differences lie in the per-frequency data — and that is precisely where thickness makes a meaningful impact.
If you need a comparison between PET panels and other absorptive materials such as wood wool board or melamine foam, The Complete 2026 Guide to Acoustic Absorbers — PET · Wood Wool · Melamine Foam Compared covers that as well.
The Real Difference in Thickness: Low- and Mid-Frequency Absorption
At high frequencies (1,000 Hz and above), all three thicknesses perform similarly — absorption coefficients exceed 1.0 (saturation). The meaningful differences emerge in the 250–500 Hz range, where thicker panels pull decisively ahead.
Korean office intelligibility is determined by 250–1,000 Hz absorption.
PET thickness — 7 axes
Korean is vowel-centric (250–1,000 Hz speech energy) — 250 Hz absorption is the key intelligibility indicator.
| 기준 | 9T (9 mm) | 12T (12 mm) | 24T (24 mm) |
|---|---|---|---|
| NRC | |||
| 250 Hz α | 0.34 | 0.39 | 0.57 |
| 500 Hz α | 0.72 | 0.82 | 0.91 |
| 1,000 Hz+ α | ≥ 1.0 | ≥ 1.0 | ≥ 1.0 |
| Flame retardant | Certified (KOR) | Certified (KOR) | Certified (KOR) |
| Weight (per ㎡) | 2.0 kg | 2.4 kg | 4.0 kg |
| DIN 18041 | Group B (corridors) | Group B4 (office) | Group A3–A4 (meeting) |
| Recommended | Small (≤ 30㎡) | Medium (30–100㎡) | Large (100㎡+), ceiling |
In Summary
The difference in NRC as a single number is only 0.05, but in the 250 Hz band — critical for Korean speech intelligibility — the absorption coefficient rises from 9T to 24T by 0.34 → 0.57 (a 67% increase).
Thickness selection is best matched to space size, use, and DIN 18041 Group criteria: 9T is the first recommendation for small offices of 30 m² or less, 12T for general offices and educational spaces, and 24T for meeting rooms, auditoriums, and studios.
Which thickness for which space
Small offices, corridors, partitions
Spaces ≤ 30 ㎡ — weight and lightweight install matter more than maximum absorption.
DIN 18041 Group B (corridors). 2.0 kg/㎡ keeps wall depth and weight minimal.
Open-plan offices, classrooms, co-working
Medium spaces 30–100 ㎡ — Korean speech vowel band 250–1,000 Hz.
DIN 18041 Group B4 (office). Best balance of absorption, weight, and install ease.
Meeting rooms, lecture halls, studios, ceilings
Large spaces 100 ㎡+ or rooms needing very low reverberation.
DIN 18041 Group A3–A4 (meeting/lecture). Bass build-up controlled for studios.
Frequently Asked Questions
Q1Which thickness is best for a typical open-plan office?
Q2Is fire-retardant certification mandatory?
Q3Is there a noticeable difference between NRC 0.79 and 0.84?
Q4Why does thickness matter more for Korean speech?
Q5What is DIN 18041 Group B4?
Glossary
- NRC (Noise Reduction Coefficient) — Arithmetic mean of sound absorption coefficients at four octave bands: 250 / 500 / 1,000 / 2,000 Hz. Rounded to the nearest 0.05. Single value between 0 and 1.
- DIN 18041 — German standard for indoor acoustic design (2016 revision). Classifies spaces into Group A (auditoriums, classrooms) and Group B (offices, corridors). Group B requirements are defined by the absorption area to room volume ratio A/V.
- ISO 354 (2003) — International standard for measuring the sound absorption coefficient of materials in a reverberation room. Compares reverberation time of an empty room with that after specimen installation, then calculates equivalent absorption area using the Sabine formula.
- KS F 2805 (2014) — Korean reverberation room sound absorption measurement standard. Aligned with ISO 354. The measurement basis for KCL-issued certified test reports.
- ASTM C423 — US reverberation room sound absorption measurement standard. Measures 18 one-third octave bands from 100 to 5,000 Hz. The primary basis for NRC calculation.
- KCL (Korea Conformity Laboratories) — An accredited Korean testing institution. The body that issued the NRC test reports for these PET panels.
- A/V — Equivalent Absorption Area (m²) divided by room Volume (m³). Adopted by DIN 18041 Group B as the acoustic quality criterion for offices and corridors. Indicates absorption area per cubic metre of space.
References
The absorption values and standard numbers in this article can be verified against the following primary sources.
- ISO 354:2003 — Acoustics, Measurement of sound absorption in a reverberation room
- KS F 2805:2014 — Measurement of sound absorption in a reverberation room (SAI Global)
- ASTM C423 — Standard Test Method for Sound Absorption (Intertek)
- NRC (Noise Reduction Coefficient) — Wikipedia
- DIN 18041:2016 — Acoustic quality in rooms (ANSI webstore)
- DIN 18041 in offices/conference rooms/classrooms — Vital-Office