Glass wool is made by the Crown process , which is similar to the process used for mineral wool. A thick stream of glass flows from a furnace into a forehearth and by gravity into a rapidly rotating steel alloy dish, punctured by hundreds of fine holes around its perimeter. The centrifugal force expels the filaments which are further extended into fine fibres by a blast of hot air. The fibres are sprayed with a bonding agent and then sucked onto a conveyor to produce a mat of the appropriate thickness. This is cured in an oven to set the bonding agent, then finally cut, trimmed and packaged.
Glass wool is non-combustible, water repellent and rot proof, contains no CFCs or HCFCs and is available in a range of product forms:
- loose for blown cavity wall insulation;
- rolls, either unfaced or laminated between kraft paper and polythene, for roofs, within timber frame construction, internal walls and within floors;
- semi-rigid batts with water-repellent silicone for complete cavity fill of new masonry;
- rigid batts for partial cavity fill within new masonry;
- compression-resistant slabs for solid concrete or beam and slab floors;
- a laminate of rigid glass wool and plasterboard for dry linings;
- PVC-coated rigid panels for exposed factory roof linings.
(The thermal conductivity of glass wool products ranges typically between 0.031 and 0.040 W/m K at 10°C.)
The sound- and fire-resistant properties of glass wool are similar to those of mineral wool. Glass wool sound-deadening quilts, which have overlaps to seal between adjacent units, are used to reduce impact sound in concrete and timber floating floors. Standard quilts are appropriate for use in lightweight partitions and over suspended ceilings.
Resin-bonded glass wool treated with water repellent is used to manufacture some ceiling tiles which meet the Class 0 fire-spread requirements of the Building Regulations (BS 476: Parts 6 and 7) and also offer sound absorption to reduce reverberant noise levels.