Rock wool for sound insulation: what it does, and what it does not

Sound work puts rock wool inside something else: a partition cavity, a machine enclosure, or the space behind a perforated facing.

That is the generic answer. It is not enough to specify from. Leytenstone publishes no acoustic performance figure for the Vulcanite Armor range, so this post carries none, for our own product or for anyone else’s. What it carries instead is how the material is used, what the public sources say absorbs and what blocks, and which published figures do constrain the choice on a hot surface.

The sections below start with the physics, reported from named sources, before reaching anything we sell. The wider application set is in what rock wool is used for.

Absorption and blocking are two different jobs

Absorption and blocking are two different jobs, and most of the trouble on this subject comes from treating them as one.

What a porous absorber does

A 2011 NASA Glenn Research Center technical memorandum on acoustic absorption in porous materials records that where a surface is nonporous incident energy reflects back into the environment, and that where it is highly porous much of the pressure wave penetrates the material first. The mechanism it describes is frictional and viscous loss between the air in the pores and the solid ligaments, converting acoustic energy into heat, and it depends on an open pore structure. Not every highly porous material makes a suitable absorber, on that same account. The UK Health and Safety Executive names open cell foam and mineral wool as absorptive materials used within a building to reduce reflected sound.

What blocks sound: mass, decoupling and sealing

The UK Building Regulations’ Approved Document E, England’s statutory guidance on resistance to the passage of sound, states what a separating wall’s resistance to airborne sound depends on: mass per unit area for solid masonry; the mass of the leaves plus the degree of isolation achieved for cavity masonry; and, for a framed wall with absorbent material, the mass of the leaves, the isolation of the frames and the absorption in the cavity between them. Mass, then isolation, then cavity absorption, in the order the document itself sets them out, with no number attached to any of them.

HSE states the consequence plainly on its workplace design page: adding absorbent materials to walls and ceiling areas will only affect the reflected, reverberant sound, not the direct path of sound. It lists barriers and screens to block the direct path as a separate measure, and says a barrier should be of a dense material, lined with absorptive material facing the noise source. NIOSH says the same, naming brick or sheet steel. In both documents the absorptive layer is a lining on the barrier rather than the barrier itself.

Why the gaps usually decide it

The National Research Council of Canada defines flanking sound transmission as transmission between two rooms by paths other than directly through the separating assembly. Approved Document E instructs that special attention be given to detailing at the perimeter and wherever a pipe or duct penetrates the floor, to avoid air paths.

The US Federal Highway Administration’s noise barrier design handbook, a highway document rather than a plant one, says to fill any gaps or cracks in an installed barrier system with grout, caulking, backer rods or sealant, and to ensure that light cannot be seen through any part of it. NIOSH adds that all doors and openings on an enclosure should close tightly, and CCOHS lists minimising gaps in machine guards among its control measures.

Does rock wool sound insulation work?

It does one of the two jobs above and not the other, which is why it is not a standalone fix. Every source quoted above puts a porous absorber inside an assembly rather than in place of one.

Published control guidance puts the work in an order. South Africa’s Noise Exposure Regulations, 2024 list engineering measures that eliminate or reduce noise at its source, or modify the routes by which it reaches a workplace, first in the hierarchy of control measures they set out. Path treatment comes after that, and an enclosure or a partition is a path measure. Where a target has to be demonstrated rather than approached, the discipline is acoustic engineering, and what that designer needs from a supplier is the material’s temperature envelope, its reaction-to-fire data and the form it comes in.

Where a partition, an enclosure or a room has to meet a noise target, the target belongs to the assembly and is established by measurement. Sound absorption is measured in a reverberation room under ASTM C423, Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method, and under BS EN ISO 354, Acoustics: Measurement of sound absorption in a reverberation room. Airborne sound transmission through building partitions and elements is measured under ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, and rated under ASTM E413, Classification for Rating Sound Insulation.

That is why the question people usually arrive with, which material to buy for soundproofing, is the wrong question asked in good faith: a figure produced under any of those methods is a test result for a defined construction. Approved Document E makes the same point from the site end, setting out performance standards to be demonstrated by pre-completion testing of the finished construction.

Where a wired blanket is fitted when noise is part of the job

Machine enclosures: generators, compressors and pump sets

The enclosure case is the barrier rule from the section above, wrapped round the machine. CCOHS records that an enclosure can be total or partial, and that partial enclosures are preferred where worker access is required.

HSE draws the boundary in its guidance on acoustic refuges: a refuge is designed much like an acoustic enclosure, but because its purpose is to keep noise out rather than in, lining the inner surfaces with acoustic absorbent material will not be necessary.

A peer-reviewed study of perforated facings records that thin impervious layers, cloths or perforated plates are usually used with fibrous absorbing materials to stop small particles becoming dislodged and polluting the environment, and cautions that such facings can affect the acoustical behaviour of the backing material. In one HSE case study absorbent units were fitted in a perforated steel case with plastic wrapping to keep oil out. A blanket fitted into an enclosure sits behind a facing of that kind rather than in the airstream.

One constraint no published guidance covers decides the material question on an engine: an enclosed engine makes heat, and the ventilation path has to survive whatever is fitted inside the box. We supply material, not enclosures: we do not design, build or specify them.

Exhaust runs, valves and letdown stations

On an exhaust run, a valve station or a letdown station the surface is hot as well as noisy, and where a wired mat is already fitted for the heat it is the same blanket. Published gas temperatures for those runs, and the grade each selects, are in what rock wool is used for. Cladding over a wired mat is detailed for water rather than for noise, and water reaching the metal is the mechanism set out in corrosion under insulation and chloride on stainless steel.

Plant rooms, ducts and partition cavities

In a plant room or on duct casing, a blanket is fitted against the casing or into the void and held by its mesh under cladding. In a framed partition it goes between the leaves. Those describe where it is put, not what results.

Read together, HSE’s and NIOSH’s barrier guidance describes the absorptive layer as a lining on a dense barrier rather than as the barrier, and Approved Document E places absorption in the cavity between a framed wall’s leaves. That is our reading of the two sources rather than something either says in so many words, and on that reading a porous blanket is a component inside an assembly.

The constraints that eliminate a material before acoustics is considered

On a hot or fire-constrained surface, two published constraints remove candidates before anyone reaches the acoustic question: the temperature the material is rated to, and how it behaves in a fire.

Temperature: the figure that selects the grade

Vulcanite Armor is supplied in three grades, each with its own published hot-surface performance per ASTM C411 / C447. Density is measured per EN1602, and the grade is selected against the hot face you measure rather than against the equipment type.

Grade	Density (EN1602)	Published hot-surface performance
rock wool blanket 80 kg/m³	80 kg/m³	650°C per ASTM C411 / C447
rock wool blanket 100 kg/m³	100 kg/m³	700°C per ASTM C411 / C447
rock wool blanket 120 kg/m³	120 kg/m³	750°C per ASTM C411 / C447
Vulcanite ProTherm ceramic fibre blanket	96 kg/m³	Working temperature 1050°C, specify against this. Classification temperature 1260°C is not a use temperature

The range is rated up to 750°C. The 750°C figure belongs to Blanket 120 and to no other grade, and parameters for the three Vulcanite Armor grades are published per grade.

Reaction to fire, and what it does not mean

Vulcanite Armor publishes a Flame Spread Index of 0 and Smoke Developed 20, tested per ASTM E84, and is compliant with ASTM C592 Type I and III. The datasheet’s own printed wording is that it holds ISO, CE and A1 certification approval.

That is reaction-to-fire data for a material, and it stops there. BS EN 13501-1:2018 classifies construction products using data from reaction to fire tests. A fire-resistance rating belongs to an assembly, and none of the figures above is one. The classes are compared in rock wool vs glass wool vs ceramic fibre.

What the datasheet says about sound, and what it does not

The Vulcanite Armor datasheet describes the blanket as suitable for thermal and acoustic insulation, and that sentence is the whole of the claim.

The published application list for rock wool blanket 80 kg/m³ uses the same phrasing: thermal and acoustic insulation of large-diameter piping, ducts and vessels where the hot-face temperature does not exceed 650°C.

Suitability in a particular installation is established by test on that installation, not by the material’s category. No acoustic performance figure is published for the Vulcanite Armor range.

ISO 15665:2023, Acoustics: Acoustic insulation for pipes, valves and flanges, is what an industrial pipe specification will call for. This range is not published against it. Where a specification calls for a class under it, the demonstration is a test on the constructed system, commissioned by the acoustic designer.

Noise at work is governed by the Noise Exposure Regulations, 2024, made under the Occupational Health and Safety Act, 1993, whose regulation 18 repealed the 2003 hearing loss regulations on 6 September 2026. They set exposure limits, and meeting one is a duty on the employer that belongs to the installed plant rather than to any material in it.

Density and thickness: installation practice, not a rated outcome

What density is on this range

Density is the grade label, and it travels with the published temperature figure rather than standing on its own. Vulcanite Armor is supplied at 80, 100 and 120 kg/m³, measured per EN1602. How the fibre is made, and how density is set, is in what rock wool is made of.

Density on its own does not set a thickness, does not set the temperature limit without the test method beside it, and is not an acoustic rating. Which grade a duty selects, and the thickness band with it, is worked through in choosing rock wool density and thickness.

What actually sets thickness in an enclosure or a cavity

On a job, thickness is set by physical constraints: the depth of the cavity or void behind the facing, the fixing method and what it will carry, the clearance to the hot surface and to moving parts, and the roll thicknesses published. On a hot line the heat calculation sets it too, under ASTM C680, and that is a separate exercise.

No thickness-to-acoustic-outcome relationship is published for this range, and this post gives no acoustic thickness rule. Where an assembly has to meet a target, thickness is part of what the acoustic designer specifies and tests.

Width, mesh and cutting

Vulcanite Armor is a wire-mesh stitched blanket on galvanised or stainless steel mesh, supplied at published widths of 600 and 1200 mm and thicknesses of 30 to 100 mm, and cut from the roll on site. Chloride ion content is 5 ppm or less, and the datasheet states that it conforms to the stainless steel corrosion specification as per ASTM C692 and C871 test method. Prices per roll are on the published price list.

Panels, boards, slabs, batts, ceiling rolls, baffles, barriers and preformed pipe sections exist in the market and are not part of this range.

Getting the grade for your line

HSE’s and NIOSH’s guidance keeps the blocking job with mass, isolation and sealing, and puts a porous blanket inside an assembly as a lining rather than as the barrier.

What we publish is the temperature envelope per grade, the reaction-to-fire data, the chloride figure and the form it comes in. Download the Vulcanite Armor datasheet for the published parameters on all three grades.

If you have the application, the measured hot-face temperature and the enclosure or casing dimensions, get a quote and we will confirm the grade and a thickness band.