Glass Wool Insulation — Blanket, Board & Acoustic

Glass wool insulation — also called fiberglass insulation or glass fiber wool — is a lightweight thermal and acoustic insulation made from recycled glass and silica sand spun into fine fibers. It delivers low thermal conductivity, A1 non-combustibility and excellent sound absorption, at a lower cost per square metre than rock wool or ceramic fiber.

Most glass wool today is made by the centrifugal glass wool process, which produces finer, more resilient fibers than older flame-attenuation methods. That finer fibre is why modern glass wool is softer to handle, absorbs sound better, and holds its thermal performance at lower density.

Rosetexwool manufactures glass wool in rigid and flexible forms for building, HVAC and industrial applications:

• Glass wool blanket — flexible rolls and mats for large-area thermal and acoustic insulation
• Glass wool board — rigid panels with higher compressive strength for walls, ducts and equipment

Key properties

• Temperature range: -120 °C to 400 °C (continuous service)
• Thermal conductivity: λ ≈ 0.036 W/(m·K) at 25 °C — low heat loss
• Fire rating: A1 non-combustible to EN 13501-1 — it does not burn or feed a fire
• Acoustic: NRC up to 0.95 — among the best sound absorbers in its price range
• Density: 10–100 kg/m³, matched to the duty
• Form: blanket, mat, board and panel (cut-to-size available)

Is glass wool fire safe? Fire rating explained

This is the question we are asked most often, and the short answer is yes: glass wool is a non-combustible insulation. It is classified Euroclass A1 under EN 13501-1 and Class A under ASTM E84, which is the highest reaction-to-fire class in both systems.

What that means in practice:

• Does glass wool catch fire? No. The fibres are inorganic glass. They do not ignite, do not support combustion, and add no fuel to a fire.
• Does it give off toxic smoke? An unfaced glass wool product does not contribute significant smoke. This is why fire rated glass wool board is widely specified for smoke exhaust ducts, escape corridors, shaft walls and fire-rated partitions.
• What does happen in a fire? Glass wool does not burn, but it does soften. The fibres begin to lose their structure somewhere around 500–600 °C, well above its 400 °C continuous service limit but far below the melting point of rock wool.

Where the limit matters. A1 non-combustibility describes how the material behaves in a fire — it does not make glass wool a high-temperature insulation. Its continuous service ceiling is 400 °C. Above that, choose rock wool (up to 650 °C), calcium silicate (up to 1100 °C) or ceramic fiber (up to 1430 °C). If your specification calls for a fire barrier that must stay structurally intact through a prolonged high-temperature fire, rock wool is the safer call.

Types of glass wool: blanket, board, mat and pipe

Choosing the right form matters as much as choosing the right material. Each format is built around a different installation reality.

Glass wool blanket (roll)

The most widely used form. Supplied compressed in rolls, typically 10–48 kg/m³, in thicknesses from 25 mm to 200 mm. It is light, cuts with a knife, and drapes over irregular surfaces — which is why a glass wool blanket is the default for steel-structure roofs, large wall areas, lofts and HVAC plenums. Faced with aluminium foil it also becomes a vapour barrier and reflects radiant heat.

Glass wool board

Rigid, dimensionally stable panels, typically 24–100 kg/m³, with far higher compressive strength than blanket. Glass wool board is the right choice where the insulation has to hold a shape or carry load: ductwork linings, wall panels, acoustic ceiling tiles, sandwich panels and equipment lagging. It is also the form normally used for fire rated glass wool board in smoke exhaust and shaft applications.

Glass wool pipe sections

Pre-formed half-shells for pipework. On long straight runs they are faster and neater than wrapping blanket, and they hold a consistent thickness around the circumference.

Facings and finishes

Any of the above can be supplied unfaced, or with a facing chosen for the environment:

• Aluminium foil — vapour barrier plus radiant-heat reflection; the standard choice for moisture control
• Kraft paper — economical, for dry internal applications
• Glass tissue / black tissue — for acoustic applications where the surface must stay permeable to sound
• Waterproof membrane — where the insulation will see weather or wash-down

All forms are normally supplied in the natural brown-to-yellow tone of glass wool, and can be cut to size on request.

Is glass wool waterproof?

Standard unfaced glass wool is not waterproof — and it is worth being precise about this, because the distinction decides whether your insulation lasts.

Glass wool fibre itself does not absorb water into the glass. But the air-filled pore structure between the fibres will hold moisture if water can get in, and wet glass wool loses most of its thermal value. A saturated blanket is roughly as good an insulator as no insulation at all.

So "waterproof glass wool" is not a property of the fibre — it is a property of the build-up. Three things deliver it:

1. Hydrophobic treatment — a water-repellent agent is added during manufacture, giving a water-repellency rate of 98% or better and keeping water absorption very low.
2. A facing — aluminium foil or a waterproof membrane laminated to the surface. Foil is the most common, and it doubles as a vapour barrier.
3. Correct detailing — sealed joints (foil tape, minimum 50 mm overlaps), staggered seams, and continuity at penetrations. Most moisture failures are workmanship failures, not material failures.

Where you need it. Ductwork, cold lines, external walls, roofs, below-grade work, anywhere with high humidity or wash-down. Where you don't. Dry internal partitions and ceiling voids, where an unfaced product is cheaper and performs identically.

Tell us the environment and we will specify the facing — or tell you honestly that you don't need one.

Acoustic glass wool: sound absorption performance

Glass wool is one of the most cost-effective sound absorbers available, and acoustic glass wool is often specified for its noise performance even where thermal insulation is not the point.

The mechanism is simple: sound enters the open fibre structure, and friction converts acoustic energy into a negligible amount of heat. Because the fibres are fine and the pore structure is open, glass wool is especially effective at mid-to-high frequencies — speech, machinery whine, and the reverberant noise that makes large spaces uncomfortable.

Typical performance:

• NRC 0.70–0.95 depending on density and thickness
• Higher density and greater thickness both improve absorption, and improve low-frequency performance in particular
• An air gap behind the insulation is one of the cheapest ways to improve low-frequency absorption

Common acoustic applications: recording studios, cinemas and theatres, open-plan offices, conference rooms, classrooms, acoustic enclosures around generators and compressors, HVAC duct lining and attenuators, and machinery-room wall and ceiling linings.

For purely acoustic duties, a black glass-tissue facing is usually the right finish — it keeps the surface acoustically transparent while containing the fibres. If a space needs both absorption and a vapour barrier, we will tell you where each facing belongs, because putting foil on the wrong side will undo the acoustic performance.

How centrifugal glass wool is made

If you have seen the term centrifugal glass wool and wondered whether it is a different product, it isn't — it is the manufacturing route that produces almost all modern glass wool, and it is worth knowing why it matters.

The process, in brief:

1. Melting — recycled glass cullet, silica sand, limestone and soda ash are melted at roughly 1360–1400 °C.
2. Fiberising — the molten glass flows into a high-speed centrifuge with thousands of holes in its side wall. Centrifugal force throws the glass out as fine streams, which high-velocity hot air stretches into fibres.
3. Binding — a binder and, where specified, a hydrophobic agent are sprayed onto the fibres as they fall.
4. Collecting and curing — the wool is gathered on a conveyor, compressed to the target density and thickness, cured in an oven, then cut to size.

The result is a fibre typically 5–8 µm in diameter, with very low shot content. Finer fibre means better resilience, lower thermal conductivity at a given density, and softer handling — which is why centrifugal glass wool outperforms older coarse-fibre products at the same weight.

Formaldehyde free glass wool

The binder is the one part of the process that is organic, and it is where emissions come from. Modern binders are available in formaldehyde-free formulations, with no added formaldehyde, dyes or colours.

We supply formaldehyde free glass wool where indoor air quality is part of the specification — schools, hospitals, offices, residential projects, and any job working to a green building rating. If your project requires formaldehyde-free material, say so when you enquire; it affects the binder we run, not the fibre.

Glass wool vs rock wool: which do you need?

Both are non-combustible mineral wool insulations, and both are Class A1 to EN 13501-1. The chemistry is not what separates them — the differences are temperature, weight, strength and price.

Choose glass wool when the duty is at or below 400 °C, weight and handling speed matter, the application is dry or correctly faced, and cost per square metre is under pressure. It is the standard choice for building envelopes, HVAC ductwork and acoustic treatment.

Choose rock wool when you need a fire barrier that holds integrity at high temperature, compressive strength, or reliable water resistance without a facing — fire-rated walls and floors, industrial plant, external insulation and high-temperature pipework.

Above 650 °C, neither is the answer: that is calcium silicate (up to 1100 °C) or ceramic fiber (up to 1430 °C) territory.

If you are unsure, send us the operating temperature and the mechanical conditions. We will tell you which one actually fits — including when the cheaper glass wool is the wrong call.

Applications — thermal & acoustic insulation

Glass wool is the workhorse of building and HVAC insulation, used for heat insulation and sound insulation alike:

• Building thermal insulation — walls, roofs, floors and partitions
• Acoustic insulation — acoustic glass wool for studios, offices, cinemas and machinery enclosures (noise control)
• HVAC & ductwork — pipe and duct lagging, smoke exhaust ducts and attenuators
• Industrial equipment — tanks, vessels and ovens up to 400 °C
• Fire-rated assemblies — fire rated glass wool board for shafts, escape routes and compartment walls

Why buy from Rosetexwool

As a glass wool manufacturer and supplier with our own factory (since 1982), we serve distributors, contractors and OEMs directly:

• ISO 9001 certified production with full traceability
• Factory-direct pricing — save up to 30% vs trading companies
• Custom density, thickness and facing (aluminium foil, kraft, glass tissue, waterproof membrane)
• Formaldehyde-free binder available on request
• Export to 30+ countries with fast global delivery
• 24-hour quotation on blankets, boards and panels

Send us your operating temperature, dimensions and quantities for a same-day quote.