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.

By Dhruv Agarwal · · 1 min read

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

PropertyTypical specification
StandardIS 8183, bonded mineral wool
Thermal conductivityApproximately 0.032 — 0.040 W/mK
Density range12 — 48 kg/m³ typical
Fire classA1 / A2 to EN 13501-1 by product and facing
FacingPlain, reinforced foil, tissue, or black glass tissue
Service temperatureLower than rock wool

Density by application

ApplicationDensity
Duct wrap, external16 — 24 kg/m³, foil faced
Duct lining, internal acoustic32 — 48 kg/m³, tissue faced
Ceiling plenum blanket12 — 16 kg/m³
Partition acoustic infill24 — 48 kg/m³
Pipe sectionPreformed, 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.

Standards referenced

  • IS 8183 — Bonded mineral wool (Bureau of Indian Standards)
  • EN 13501-1 — Reaction to fire classification (CEN-CENELEC)
  • ECBC 2017 — Building envelope and services insulation (Bureau of Energy Efficiency)

Frequently asked

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.

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.

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.

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