# Glass Wool Insulation for Ducts, Ceilings and Walls

> Glass wool is mineral fibre spun from molten glass and bound into rolls, slabs and pipe sections, used for duct wrap, internal duct lining, ceiling plenum blankets and partition infill. It is lighter and cheaper than rock wool with slightly better thermal performance per millimetre, but lower temperature tolerance.

## What it is

**Mineral fibre spun from molten glass**, bound into rolls, slabs and pipe
sections. Lighter and cheaper than rock wool, with slightly better thermal
conductivity per millimetre and lower temperature tolerance.

## Specification at a glance

| Property | Typical specification |
| --- | --- |
| Standard | IS 8183, bonded mineral wool |
| Thermal conductivity | Approximately 0.032 — 0.040 W/mK |
| Density range | 12 — 48 kg/m³ typical |
| Fire class | A1 / A2 to EN 13501-1 by product and facing |
| Facing | Plain, reinforced foil, tissue, or black glass tissue |
| Service temperature | Lower than rock wool |

## Density by application

| Application | Density |
| --- | --- |
| Duct wrap, external | 16 — 24 kg/m³, foil faced |
| Duct lining, internal acoustic | 32 — 48 kg/m³, tissue faced |
| Ceiling plenum blanket | 12 — 16 kg/m³ |
| Partition acoustic infill | 24 — 48 kg/m³ |
| Pipe section | Preformed, density by diameter |

## Where it belongs on a fit-out

**Duct wrap** on conditioned-air and chilled-water ducts, foil faced for vapour
control. **Internal duct lining** where fan and airflow noise must be absorbed
before it reaches the occupied space. **Partition infill** between meeting
rooms and tenancies, where the acoustic rating of the partition depends on it.
**Above ceiling**, as a plenum blanket where the slab soffit is uninsulated.

## Where projects go wrong

- **Unfaced insulation on a cold duct.** Condensation forms inside the
  insulation, performance collapses, and ceilings stain below.
- **Foil joints untaped.** The vapour barrier is only continuous if the laps
  are sealed; an untaped lap is an open path.
- **Insulation compressed by a cable tray or hanger.** Compression reduces
  thickness and performance at exactly the points nobody inspects.
- **Glass wool used as a cavity barrier.** It is not the specified material for
  that duty; rock wool is.

## Standards referenced

Bonded mineral wool under **IS 8183**. Reaction-to-fire classification to
**EN 13501-1**. Services and envelope insulation requirements under
**ECBC 2017**.

## Frequently asked questions

### Glass wool or rock wool — which should be used?

Glass wool is lighter, cheaper and slightly better per millimetre thermally, so it suits duct wrap, ceiling plenum blankets and partition infill. Rock wool withstands far higher temperatures and holds its form better at density, so it is required for cavity barriers, ventilated facade slabs and high-temperature plant. Where fire or form-stability governs, use rock wool; where cost and general thermal or acoustic infill govern, glass wool is appropriate.

### What facing should duct insulation have?

Reinforced aluminium foil, for two reasons. It acts as a vapour barrier, which matters on chilled-water and conditioned-air ducts where condensation would otherwise form within the insulation, and it gives a serviceable surface that can be taped at joints. Unfaced glass wool on a cold duct in Indian humidity will wet through and lose most of its performance.

### Does glass wool settle over time?

Lower density rolls can settle in vertical cavities over years, leaving an uninsulated gap at the top. Where a vertical application must hold its position for the life of the building, specify a higher density slab or a rock wool board rather than a light roll, and support it mechanically rather than relying on friction fit.

## Sources

- [IS 8183](https://standards.bis.gov.in/website/published-standards/department-wise) — Bonded mineral wool
- [EN 13501-1](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Reaction to fire classification
- [ECBC 2017](https://beeindia.gov.in/) — Building envelope and services insulation

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Source: https://hagerstone.com/materials/glass-wool-insulation