Acoustic Underlay for Carpet UK: Rubber vs Foam, Which Is Better?

When fitting carpet in a flat, converted property, or any multi-storey building, the underlay you choose has a direct impact on how much impact noise travels between floors. Rubber acoustic underlay delivers significantly better sound insulation than foam or felt alternatives — and this guide explains exactly why, how to choose the right product, and what to expect from the installation.

What Does Carpet Underlay Actually Do Acoustically?

Carpet alone provides some acoustic benefit — the pile absorbs airborne sound reflections and the backing offers minor impact dampening. However, the underlay beneath the carpet does the heavy lifting for structural impact noise reduction.

When someone walks across a carpeted floor, their footstep generates an impact pulse. Without underlay, that pulse travels directly through the subfloor structure. With an acoustic underlay, the layer absorbs and dissipates the energy before it reaches the floor deck, reducing the sound that radiates into the room below.

The measurable improvement is expressed as ΔLw (delta Lw, in dB) — a higher value means greater improvement. Standard domestic foam carpet underlay achieves ΔLw 10–14 dB. Our rubber acoustic underlays achieve ΔLw 17–28 dB at equivalent or lesser thickness.

Rubber vs Foam Acoustic Underlay for Carpet: Full Comparison

Property	Rubber (Rubberco)	PU Foam	EVA/PE Foam
ΔLw (impact noise)	17–28 dB	10–14 dB	8–12 dB
Density	1,100–1,400 kg/m³	25–35 kg/m³	30–50 kg/m³
Compression set	None — retains thickness for 25+ years	Significant — degrades in 3–5 years	Moderate — 5–8 years
UFH compatible	Yes — all temperatures	Check limits (typically <27°C)	Generally no
Moisture resistance	Excellent — closed cell	Poor — absorbs moisture	Good
Part E suitable	Yes (10mm Decimat in compliant build-up)	Rarely	No
Recycled content	Up to 94% recycled rubber	Typically virgin PU	Varies
Lifespan	25+ years	3–5 years	5–8 years
Cost per m²	Higher upfront	Lower upfront	Lowest

Verdict: Rubber wins on every acoustic and durability metric. The higher upfront cost is offset by longevity — foam underlay may need replacing when the carpet is next fitted, whereas rubber outlasts multiple carpet changes.

SilentCloud FFR: Rubber Acoustic Underlay for Carpet

Our SilentCloud FFR roll is specifically designed for carpet and carpet tile installations. Key specifications:

• Thickness: Available in 3mm and 5mm
• Material: High-density recycled rubber, smooth top surface for carpet grip
• Roll widths: 1.0m and 1.4m standard; cut-to-size available
• Impact noise: ΔLw up to 21 dB (5mm)
• UFH compatible: Yes
• Applications: Domestic and commercial carpet, carpet tiles, needle-punched carpet

SilentCloud FFR replaces traditional PU foam underlay in all carpet applications while delivering double the impact noise reduction and lasting the life of the building rather than the life of the carpet.

Acoustic Underlay for Carpet Tiles

Carpet tiles present a distinct underlay challenge — they are typically loose-laid or lightly adhered and require an underlay that does not compress significantly under point loads from furniture legs or foot traffic. Rubber acoustic underlay is the correct specification for carpet tile installations for the following reasons:

• No compression set: Rubber retains its thickness under long-term static loads, maintaining both acoustic performance and carpet tile flatness
• Dimensional stability: Unlike foam, rubber does not creep or shift under traffic, preventing carpet tile edges from lifting
• Moisture resistance: In commercial settings where cleaning involves wet mopping, rubber is unaffected by incidental moisture
• Load distribution: High density distributes point loads across a wider area, reducing indentation from office chairs and heavy furniture

For carpet tile applications, we recommend 3mm SilentCloud FFR as the standard specification, upgrading to 5mm where acoustic performance requirements are higher.

Carpet Type Compatibility Table

Carpet Type	Recommended Underlay	Thickness	Notes
Woven Axminster/Wilton (domestic)	SilentCloud FFR	5mm	Premium feel; maximum impact noise reduction
Tufted carpet (domestic)	SilentCloud FFR or 3mm rubber	3mm	Standard domestic specification
Carpet tiles (commercial)	SilentCloud FFR	3mm	Loose-lay with appropriate adhesive to perimeter only
Needle-punched carpet (commercial)	SilentCloud FFR	3mm	High-traffic commercial; use 5mm for improved isolation
Loop pile (domestic/commercial)	SilentCloud FFR	3mm or 5mm	Avoid very thick underlay under loop pile — can cause rippling
Carpet over UFH	SilentCloud FFR (low tog)	3mm	Check total tog of carpet + underlay; typically <2.5 tog for UFH

Thickness Guide for Carpet Acoustic Underlay

The correct underlay thickness for carpet depends on your acoustic requirements and the subfloor construction:

• 3mm rubber: Suitable for domestic carpet in houses and maisonettes. Provides ΔLw ~17–18 dB. Correct specification where comfort and moderate sound improvement are required.
• 5mm rubber: Recommended for timber frame construction, upper floors in converted properties, and any carpet installation where the floor is identified as a separating floor. Provides ΔLw ~20–21 dB.
• 10mm Decimat: Where maximum acoustic performance is required — Part E-compliant floor build-ups in residential conversions and purpose-built flats. Not a standard carpet underlay thickness, but specified where acoustic consultants require maximum ΔLw contribution.

Installation Tips for Rubber Underlay Under Carpet

1. Fix gripper rods first: Nail gripper rods to the perimeter at the correct distance from the skirting board (typically 10mm less than carpet thickness).
2. Lay underlay with smooth face up: The smooth surface of SilentCloud FFR should face the carpet backing for best adhesion between carpet and underlay.
3. Staple or tape underlay to timber subfloors: Use a heavy-duty staple gun at 300mm centres around the perimeter and at joins. On concrete, butt joins and tape with self-adhesive underlay tape.
4. Keep underlay 10mm back from gripper rods: Do not overlay the underlay onto gripper rods — the carpet must hook onto the rod cleanly.
5. Cut with a sharp utility knife: Score and cut along a straight edge. Rubber cuts cleanly without tearing.
6. Knee-kick or power stretch the carpet: Rubber underlay provides a firmer base than foam, which may require slightly more force when power stretching. Ensure the carpet is fully tensioned before trimming.

Frequently Asked Questions

Can rubber underlay be used under all carpet types?

Yes. Rubber acoustic underlay is suitable under woven, tufted, loop pile, cut pile, and needle-punched carpet, as well as carpet tiles. The only consideration is tog value for UFH applications — check the carpet manufacturer's maximum total tog rating for the full build-up and ensure the rubber underlay's tog value (typically 0.5–1.0 tog for 3mm) plus the carpet's tog falls within that limit.

Does rubber underlay feel harder underfoot than foam?

Rubber underlay feels firmer than foam underlay of equivalent thickness — this is a function of its density. Many customers and carpet fitters report that rubber feels better quality and more stable than foam. The firmness reduces foot fatigue in commercial environments and prevents the carpet from feeling spongy. For maximum softness underfoot, specify 5mm over 3mm.

How do I join rubber underlay sheets?

Butt joins tightly — do not overlap. Secure joins on concrete with self-adhesive underlay tape applied to the top surface. On timber subfloors, staple both edges of the join to the floor at 200mm centres. Overlapping underlay creates a ridge that is visible through the carpet over time.

Can rubber acoustic underlay be re-used when the carpet is replaced?

Yes — in most cases. Rubber underlay does not compress permanently or degrade, so it can be rolled up carefully, stored, and relaid when new carpet is fitted. This is another economic advantage over foam underlay, which typically needs replacing with each carpet change. Check the underlay for tears or contamination before re-laying.

Is rubber underlay for carpet more sustainable than foam?

Yes, significantly. Our rubber acoustic underlays contain up to 94% recycled rubber — typically recycled from end-of-life vehicle tyres. This diverts waste from landfill and reduces the demand for virgin materials. Rubber also lasts 25+ years versus 3–5 years for foam, reducing the total material consumed over the life of a building. At end of life, rubber underlay can be recycled again.

Browse our full range of acoustic underlay UK — rubber sound insulation for carpet, laminate, and all floor types.