Polyester felt vs rockwool vs foam — which acoustic panel for Indian offices (2026)
An honest comparison of the three materials Indian offices keep choosing between — NRC, fire rating, lifespan, recyclability, and cost — with the cases where each one is still the right call.
An architect emailed last week. The brief was a 4,000 sq ft office floor in Whitefield — NRC 0.65 on the walls, fire compliance for the local AHJ, and “something the client can recycle when we move out in seven years.” Three quotes had come back from three suppliers: polyester felt, rockwool behind fabric, and pyramid foam. Same NRC target on paper. Three very different materials underneath.
She asked which one to spec.
This is the conversation we have most weeks. Here is the answer — with the numbers, the cost reality, and the cases where each material is still the right call.
The quick verdict
If you only have a minute, this is the table to keep.
| Polyester Felt | Rockwool (behind fabric) | Acoustic Foam | |
|---|---|---|---|
| NRC (typical install) | 0.70 to 1.00 | 0.85 to 1.05 | 0.55 to 0.95 |
| Fire rating available | Class A in FR variant | Class A standard | Class B at best |
| Off-gassing | None — inert PET | Mineral fibre, needs sealing | VOCs released for months |
| Useful lifespan | 15+ years | 25+ years if sealed dry | 3 to 5 years in India |
| Recyclability | 100% — same PET stream | None — landfill | None — landfill |
| Humidity tolerance | Unaffected to 95% RH | Loses NRC if it gets damp | Degrades faster |
| Look | Finished surface, 94 colours | Behind fabric or frame only | Industrial — exposed |
| Cost trajectory | Moderate day-one, best-in-class lifetime | Highest day-one, stable over 20+ years | Cheapest day-one, most expensive over 15 years (replacement cycle) |
The defaults that fall out of this table: polyester felt for finished offices, rockwool for industrial enclosures and theatre walls behind fabric, foam for budget bedrooms and back-of-house rooms where the look does not matter.
The rest of the post explains why.
Why polyester felt wins most Indian offices
The PET fibre that becomes acoustic felt comes from used drinking-water bottles. About 75 percent of every panel we ship is post-consumer recycled PET, including ocean-bound PET from the Mahanadi and Godavari basins. The remaining 25 percent is virgin staple fibre for tensile strength. The mat is needle-punched and thermally bonded — no chemical binders, no formaldehyde, no glue.
For an open-plan office, four things matter, roughly in this order:
1. The panel itself is the finish. Rockwool needs a fabric wrap, a frame, and an installer who can tension the cloth without showing fibres at the edges. Foam needs paint, and the moment you paint it the NRC drops. Felt is the finish. You see the colour you specified — KA-7904 bone white, KA-7905 carbon, KA-7912 forest. The 94-code library is what makes felt the architect’s first choice. No site-applied finish, no batch colour drift, no failure modes from a wrap that wasn’t tensioned right.
2. Bangalore humidity is not a problem. Felt’s NRC does not move measurably at 85 percent relative humidity. Rockwool absorbs moisture if the fabric wrap is not perfectly sealed, and its acoustic performance drops the moment it gets damp. Foam holds moisture and degrades faster — porous, open-cell foam in a humid Indian office typically loses structural integrity in four monsoons.
3. The fibre is recoverable. When the office gets re-fitted in seven years, polyester felt panels go back into the same PET recycling stream they came from. Rockwool goes to landfill. Foam goes to landfill, but also off-gases for years before it gets there. For LEED v4.1 MR1 (Building Lifecycle Impact Reduction) or IGBC Green Homes IRO-1 (Recycled Content), felt is the only one of the three that contributes meaningfully — see the GRS chain-of-custody documentation on the material page.
4. NRC of 0.85 to 1.00 in a normal install. A 12mm felt panel on a 50mm air gap reaches NRC 1.00 in the standard ASTM C423 test, with the air gap doing most of the work below 500 Hz. The cavity-depth post walks through the maths. For most offices that means one panel on the wall does the job — no fabric wrap, no frame, no engineer on site.
A side benefit nobody mentions: a 12mm felt panel weighs roughly 1.4 kg per square foot. Two installers can fit a 200 sq ft feature wall in an afternoon. The same wall in rockwool-behind-fabric is a three-person, two-day install.
When rockwool still wins
Felt is not the universal answer. Rockwool stays the right material for four cases, and pretending otherwise is dishonest.
Industrial enclosures and machine rooms. Rockwool is rated to 750 °C in the unfaced grade. Polyester felt softens at 250 °C. If the panel sits inside a generator housing, an HVAC plenum, or a transformer room, rockwool is the only correct call.
Theatre walls where the surface is fabric anyway. A black-box theatre or a Dolby Atmos screening room hides the panel behind tensioned acoustic fabric for sightline reasons. The fabric is the finish; the absorber behind it is irrelevant to the audience. Rockwool gives slightly higher NRC at low frequencies (better bass-trap performance) and meets Class A fire rating off the shelf with no FR additive. For deep-frequency theatre treatment, this matters.
Acoustic isolation systems. When you need both mass (to block transmission) and absorption (to reduce reverberation inside), rockwool sits between a double-stud wall and contributes to both. Felt is purely absorptive and does not add transmission loss. The two materials solve different problems — and the acoustic vs soundproofing post walks through that distinction in detail.
HVAC duct liner. Open-cell foam liners shed particles into the airstream over time. Rockwool with a perforated metal facing is the standard for ducted office HVAC and remains so.
When foam is the wrong answer
Acoustic foam — the pyramid and wedge profile most people picture when they hear “acoustic treatment” — is the cheapest of the three materials and the worst for almost every Indian office context. Three reasons:
Fire behaviour. Open-cell polyurethane foam, even with FR additives, rarely reaches better than Class B in IS 6329 or BS 476 Part 7. In a fire, it releases hydrogen cyanide and carbon monoxide before it stops smouldering. Most Indian commercial fire codes require Class A on walls of common-use rooms. Foam fails this default.
Lifespan. UV exposure and humidity break polyurethane foam down. In an air-conditioned Indian office, a foam panel installed in 2026 will look brittle and yellowed by 2030, dusty by 2032, and ready to fall off the wall by 2033. The TCO calculation rarely favours foam once you include the replacement.
The look. Pyramid foam reads “studio.” On the wall of a board room, it reads cheap. Architects almost never specify it for client-facing rooms once they have seen what felt looks like next to it.
Where foam is still defensible: a podcast booth or home recording closet on a tight budget, where the user accepts the look, the room is small enough that fire risk is contained, and the panels will be replaced in three years anyway. For that case — and only that case — foam is a reasonable choice.
The fire-rating reality
Most “fire-rated acoustic panel” claims in the Indian market sit on shaky paperwork. The two questions that separate a real fire rating from a marketing one:
- Which standard, which class? IS 6329 / IS 8183 (Indian), BS 476 Part 6/7 (British), ASTM E84 (US) — each grades from Class 1/A (best) downward. “Fire rated” alone means nothing. Ask for Class A in IS 6329 or a Class 1 BS 476 certificate.
- Whose lab? Government-recognised labs (CBRI, NABL-accredited) for IS standards; UL or Intertek for international. A test report on a supplier’s letterhead is not a certificate.
For the three materials:
- Polyester felt FR. Available in Class A IS 6329 with a small FR additive. Ask for the test report by batch number — that is what the AHJ asks for during occupancy clearance.
- Rockwool. Class A by default, no additive needed. This is rockwool’s strongest case in fire-sensitive rooms.
- Foam. Generally Class B even with additives. Some imported variants claim Class A but the certificates are usually overseas — and the Indian AHJ may not accept them.
The cost reality (over fifteen years, not on day one)
The day-one number on the quotation is the obvious comparison. It is also the wrong one, because the three materials do not last the same amount of time.
For a 1,000 sq ft office wall treatment, in relative terms:
| Day-1 cost (index) | Replacement cycle | 15-year cost (index) | |
|---|---|---|---|
| Polyester felt | 1.0x baseline | Once, year 15 if at all | 1.0x baseline |
| Rockwool + fabric | ~1.5x | Once, year 20+ | ~1.5x |
| Acoustic foam | ~0.6x | Every 4 years | ~2.4x |
Foam looks cheap on the day-one number and becomes the most expensive material over a realistic office lifecycle because it needs to be replaced roughly every four years in Indian humidity. Felt and rockwool are roughly comparable over fifteen years, but felt requires no fabric subcontractor and no second install crew. The actual rupee numbers depend on room geometry, install access and colour spec — quoted per project.
A specifier’s decision tree
Three questions get you to the right material in under a minute:
- Is the panel itself the finish? → Polyester felt.
- Will it sit behind fabric, inside a wall, or in a fire/heat-critical enclosure? → Rockwool.
- Is the budget the lowest possible, back-of-house, and will be replaced in three years? → Foam.
If the first answer is yes — which it is for ~85 percent of the office briefs we see — the rest of the tree does not apply.
Three lines, if that is all you wanted
Polyester felt is the right material for almost every Indian office wall and ceiling that needs to look finished. Rockwool is the right material when the panel hides behind fabric or sits in a fire-critical enclosure. Foam is the right material when budget and looks both stop mattering.
For most architects specifying treatment for a Bangalore, Mumbai, Delhi or Hyderabad office floor in 2026, the answer is felt — and the 94-code colour library is usually what closes the conversation.
If you want a no-cost acoustic estimate for your specific room — including which mix of panel, baffle and ceiling cloud will reach your target NRC — send the floor plan. We do this every week for architects across India.
FAQ
What is the NRC of polyester felt vs rockwool? A 12mm polyester felt panel on a 50mm air gap reaches NRC 1.00 in the ASTM C423 test. A 50mm rockwool slab behind a tensioned acoustic fabric reaches NRC 1.05 in the same test. In a normal office install, both materials sound equivalent — the difference shows up only in dedicated theatre and bass-trap applications.
Is polyester felt fire-rated for Indian offices? The FR variant of polyester felt is rated Class A under IS 6329. Ask your supplier for the batch test report, not just a letterhead claim, and confirm the certificate is from a NABL-accredited lab. KARIKA’s FR felt is Intertek-tested and the certificate is available on request.
Does rockwool cost more than polyester felt? On day one, rockwool installed behind fabric typically runs 25 to 30 percent higher than the equivalent felt install, mainly because of the wrap, the frame, and the additional install labour. Over fifteen years the two materials cost roughly the same. Foam is cheaper on day one and the most expensive over fifteen years because of the replacement cycle.
Can acoustic foam be used in a fire-rated commercial office? Most acoustic foams reach only Class B under IS 6329 even with FR additives. For a commercial office wall in a common-use room — meeting rooms, board rooms, open plan — most Indian fire codes require Class A, which rules foam out. Foam remains usable in private back-of-house rooms with low occupancy.
Which acoustic material contributes to LEED or IGBC credits? Polyester felt with documented GRS chain of custody (75 percent post-consumer recycled PET) contributes to LEED v4.1 MR1 Building Lifecycle Impact Reduction and IGBC Green Homes IRO-1 Recycled Content. Rockwool and standard acoustic foam do not. Ask the supplier for the GRS 4.0 scope certificate by mill, not a general claim.
Is rockwool dangerous to handle? Modern stone wool is not classified as a carcinogen and is regulated as a low-bio-persistent fibre under EU directive 97/69/EC. It does cause mechanical skin irritation during install, which is why it almost always sits behind a wrap. In a finished office wall, this is not a user-facing concern.
Where can polyester felt be used outdoors? Polyester felt is UV-stable in shaded outdoor applications — covered terraces, soffits, deep verandahs. Direct sun exposure for years will fade the colour and reduce the surface integrity. For exposed outdoor acoustic treatment, neither felt, rockwool nor foam is the right material — perforated metal cassettes with mineral fibre cores are the correct choice.