Cork absorption coefficient
Cork tile absorbs α 0.03 at 500 Hz — NRC 0.05, the same rating as an unglazed brick wall. Cork is sold almost everywhere as an acoustic material, and on measured absorption data it is not one: it sits with the reflective hard surfaces in this database, not with the treatment. Here are the sourced octave-band coefficients (α) for cork and the surfaces it actually resembles, pulled straight from our absorption database, the arithmetic showing how much cork it would take to replace one panel, and the one job cork genuinely does well. We don't sell panels or building materials.
Cork and hard-surface absorption coefficients by octave band
Random-incidence coefficients measured per ISO 354 / ASTM C423. α is the fraction of incident sound energy absorbed (1.00 = fully absorbed). NRC is the average of the 250 / 500 / 1000 / 2000 Hz values. The point of this table is the company cork keeps: read across and it is indistinguishable from masonry and plasterboard.
| Surface | 125 Hz | 250 Hz | 500 Hz | 1k Hz | 2k Hz | 4k Hz | NRC |
|---|---|---|---|---|---|---|---|
| Cork tiles, 25 mm, on solid backing | 0.02 | 0.02 | 0.03 | 0.04 | 0.04 | 0.05 | 0.05 |
| Brick, unglazed | 0.03 | 0.03 | 0.03 | 0.04 | 0.05 | 0.07 | 0.05 |
| Plaster on masonry | 0.01 | 0.01 | 0.02 | 0.03 | 0.04 | 0.05 | 0.05 |
| Gypsum board (12 mm on studs) | 0.29 | 0.10 | 0.05 | 0.04 | 0.07 | 0.09 | 0.05 |
| Marble or glazed tile | 0.01 | 0.01 | 0.01 | 0.01 | 0.02 | 0.02 | 0.00 |
Source: Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured). See every value and its source in the full database or download the CSV (CC BY 4.0). This row is specifically cork tiles, 25 mm, on solid backing — a thin tile bonded to a solid substrate, which is the form sold for walls. Thick expanded/agglomerated cork board over a cavity is a different construction and performs somewhat better; we do not hold a sourced row for it, so no figure for it is quoted here.
Cork against the materials it is sold alongside
The hard-surface comparison is the fair one, but it is not the comparison buyers are making. Cork tiles are marketed for the same job as foam and panels, so here they are side by side.
| Material | 125 Hz | 250 Hz | 500 Hz | 1k Hz | 2k Hz | 4k Hz | NRC |
|---|---|---|---|---|---|---|---|
| Cork tiles, 25 mm, on solid backing | 0.02 | 0.02 | 0.03 | 0.04 | 0.04 | 0.05 | 0.05 |
| Open-cell acoustic foam, 50 mm | 0.08 | 0.25 | 0.60 | 0.90 | 0.95 | 0.98 | 0.70 |
| Mineral wool, 50 mm, on wall | 0.15 | 0.55 | 0.90 | 1.00 | 1.00 | 1.00 | 0.85 |
| Curtains, heavy, deep folds | 0.14 | 0.35 | 0.55 | 0.72 | 0.70 | 0.65 | 0.60 |
How much cork replaces one panel?
Absorption is area multiplied by coefficient, measured in sabins, so materials with different coefficients can be compared directly by area. The question "how much cork equals one panel" therefore has an exact answer per octave band — this is simply αwool ÷ αcork:
| Octave band | Cork tile α | 50 mm mineral wool α | m² of cork per 1 m² of wool |
|---|---|---|---|
| 125 Hz | 0.02 | 0.15 | 8× |
| 250 Hz | 0.02 | 0.55 | 28× |
| 500 Hz | 0.03 | 0.90 | 30× |
| 1k Hz | 0.04 | 1.00 | 25× |
| 2k Hz | 0.04 | 1.00 | 25× |
| 4k Hz | 0.05 | 1.00 | 20× |
Across the bands that matter for speech and music clarity the ratio sits between 20× and 30×. Put in room terms, using the same reference room as our panel calculator (4 × 3 × 2.4 m):
Why cork absorbs so little
Cork looks like it should work. It is soft, light, natural and visibly cellular, and it dampens a knuckle-rap in a way that tile does not. But there are only two ways a surface can absorb airborne sound, and a cork tile on a wall has access to neither.
Porous absorption — the mechanism behind mineral wool, foam and carpet — requires air to be driven through an open, interconnected network of pores, losing energy to viscous friction along the way. That is why porous absorbers need physical depth and why they are open to the air on the front face. Cork's cells are closed: each is a sealed gas-filled pocket, which is exactly what makes cork a good thermal insulator, a good gasket and a floating bottle stopper. Air cannot flow through it, so the porous mechanism is simply unavailable.
Panel resonance — the mechanism that gives gypsum board α 0.29 at 125 Hz — requires a relatively limp sheet suspended over a trapped air cavity, so it can move as a mass on a spring. A cork tile bonded flat to a solid wall has no cavity, nothing to flex against, and far too little mass to tune usefully low. So that mechanism is unavailable too. What remains is a thin, closed, fairly stiff layer on a hard backing, which is a description of a reflective surface. The measured α 0.02–0.05 follows directly.
What cork is genuinely good for
This page is not an argument that cork is a bad material — it is an argument that it is frequently sold for the wrong problem. Cork's real acoustic application is impact noise, not absorption: as a resilient underlay beneath a floor finish, it decouples footfalls, dropped objects and furniture scrapes from the structure, so less of that energy is transmitted to the room below. That is a genuine and well-established use, and it is a completely different measurement from the one on this page — impact performance is rated by impact-isolation testing of a whole floor assembly, not by α, and depends on the entire build-up rather than the cork alone. We hold no sourced impact data, so this page quotes none.
Cork is also perfectly reasonable as a pinboard, a wall finish you like the look of, or a warm, hard-wearing floor. None of those is an acoustic claim, and none of them is in dispute here.
Absorption is not soundproofing
Cork tiles are often bought to stop noise passing between rooms. Nothing on this page speaks to that, and cork does not do it either. Blocking airborne sound through a partition is a function of mass, airtightness and decoupling — a 25 mm cork layer adds very little mass and seals nothing, so its effect on transmission is small. A material's absorption coefficient describes what happens to sound inside the room it is fitted in; it says nothing about what passes through the wall. See what the absorption coefficient actually measures for the general case.
What to use instead
- For echo and reverberation: a porous absorber with real depth. 50 mm mineral wool is α 0.90 at 500 Hz — 30× cork — and thickness is the main lever. See mineral wool.
- If you want soft furnishing rather than panels: heavy curtains in deep folds reach α 0.55 at 500 Hz and heavy carpet on a pad 0.57 — both far ahead of cork. See curtains and carpet.
- For bass: none of the above, and certainly not cork at α 0.02 at 125 Hz. Low frequencies need depth — start with the porous absorber calculator.
- For footstep noise reaching the room below: cork underlay is a legitimate choice — but that is an isolation project, not a treatment one.
Plan the rest of your room
If cork was going to be your treatment, the useful next step is to size the real thing. The acoustic panel calculator gives a panel count and placement for your room's dimensions, the RT60 calculator lets you set cork (or any material in the database) as a surface and see the per-band result against a reverberation target, and the room mode calculator finds the low-frequency problems that no wall covering of any kind will fix.
Frequently asked questions
What is the sound absorption coefficient of cork?
For cork tiles, 25 mm, on solid backing the sourced octave-band coefficients are α 0.02 / 0.02 / 0.03 / 0.04 / 0.04 / 0.05 at 125 / 250 / 500 / 1000 / 2000 / 4000 Hz, giving an NRC of 0.05. Those values are close to the bottom of the scale at every frequency: cork tile absorbs between 2% and 5% of the sound energy that reaches it, and reflects the rest.
Does cork absorb sound?
Barely. At NRC 0.05 a cork tile wall is rated the same as unglazed brick (NRC 0.05), plaster on masonry (NRC 0.05) and gypsum board (NRC 0.05) — all of which are treated as reflective surfaces in any room calculation. Cork is widely sold as an acoustic material, but on measured absorption data it belongs with the hard surfaces, not with the treatment.
How much cork equals one acoustic panel?
At 500 Hz, cork tile is α 0.03 against α 0.90 for 50 mm mineral wool — a factor of 30. Because absorption is area × coefficient, you would need about 30 m² of cork to match 1 m² of mineral wool. Covering all four walls of a 4 × 3 m room (33.6 m² of cork) buys 1.01 sabins at 500 Hz — less than 2 standard 60 × 120 cm mineral-wool panels.
Do cork wall tiles soundproof a room?
No. Soundproofing means stopping sound passing through a partition, which takes mass, sealing and decoupling — a 25 mm cork tile adds very little mass and no decoupling. Absorption and isolation are different problems, and cork happens to be weak at both when it is glued to a wall. Its genuine acoustic use is elsewhere: as a resilient underlay it reduces impact noise (footsteps) transmitted into the structure below.
Why does cork absorb so little when it looks porous?
Because cork's cells are closed. Porous absorption needs air to move through an open, interconnected structure and lose energy to friction against the fibres — that is how mineral wool reaches α 0.90. Cork's sealed cells do not let air pass, and a tile bonded to a solid backing has no cavity to flex into either, so neither of the two absorption mechanisms is available to it. It looks like a soft material and behaves acoustically like a thin hard one.
What should I use instead of cork for room acoustics?
Any genuine porous absorber with depth. At 500 Hz, 50 mm mineral wool is α 0.90 and 50 mm open-cell acoustic foam is α 0.60, against cork's 0.03. Heavy curtains in deep folds reach 0.55 and heavy carpet on a pad 0.57. Any of these does more in a square metre than cork does in 30.
Related material guides
- Acoustic foam absorption coefficient — NRC by thickness and foam type — and why it barely touches bass.
- Mineral wool absorption coefficient — Thickness and an air gap beat density — the panel-builder’s material.
- Carpet absorption coefficient — Tames echo, not bass — and why it is not soundproofing.
- Curtains absorption coefficient — Fullness and an air gap are the levers — “soundproof” curtains do not block noise.
- Gypsum board (drywall) absorption coefficient — The one surface in the room that absorbs bass rather than treble — and NRC 0.05 hides it.
- Concrete absorption coefficient — Four different materials share the name — and painting the block costs you most of it.
What the numbers mean: what is the sound absorption coefficient? · New here? Start with Acoustic Treatment 101 · Browse all material absorption data · See our methodology & sources.