--- title: "Glass Wool - GWP and renovation use" canonical_url: https://fremtidenstegnestue.dk/en/knowledge/materials/glasuld markdown_url: https://fremtidenstegnestue.dk/en/knowledge/materials/glasuld.md author: "Fremtidens Tegnestue" page_type: material primary_intent: "Explain use, GWP and renovation relevance for Glass Wool." primary_keyword: "Glass Wool" audience: "Homeowners, studios and agents researching material choices." summary: "Glass wool is made from melted glass — typically with up to 80% recycled glass — and spun into fine fibres. It is light, inexpensive, and has good insulating capacity. Used primarily for attic insulation and lightweight facade constructions. Carbon footprint is lower than rock wool because the melting temperature is lower." source_basis: - "ECO Platform EPD average" - "Social- og Boligstyrelsen: Klimakrav og LCA i bygningsreglementet: https://www.sbst.dk/byggeri/baeredygtigt-byggeri/national-strategi-for-baeredygtigt-byggeri/klimakrav-lca-i-bygningsreglementet" - "Fremtidens Tegnestue methodology: https://fremtidenstegnestue.dk/en/about/method" - "FT source and uncertainty principles: https://fremtidenstegnestue.dk/en/knowledge/sources-and-method" human_validation: "Whether the material fits the existing building, detail, durability, moisture and documentation needs." responsibility_line: "AI can prepare, compile and flag uncertainty. The architect validates the consequences." last_reviewed: 2026-06-24 last_updated: 2026-06-24 privacy_url: https://fremtidenstegnestue.dk/en/privacy related_pages: - url: https://fremtidenstegnestue.dk/en/knowledge/materials/mineraluld relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials/celluloseisolering relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials/hoer-isolering relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials relation: hub - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/lca relation: concept status: published --- # Glass Wool - GWP and renovation use Canonical URL: https://fremtidenstegnestue.dk/en/knowledge/materials/glasuld Markdown URL: https://fremtidenstegnestue.dk/en/knowledge/materials/glasuld.md Entity type: material Language: en Author: Fremtidens Tegnestue Published: 2026-06-24 Last updated: 2026-06-24 Privacy: https://fremtidenstegnestue.dk/en/privacy ## Short answer Glass wool is made from melted glass — typically with up to 80% recycled glass — and spun into fine fibres. It is light, inexpensive, and has good insulating capacity. Used primarily for attic insulation and lightweight facade constructions. Carbon footprint is lower than rock wool because the melting temperature is lower. ## Who it is relevant for Homeowners, studios and agents researching material choices. ## What FT can prepare - Summarise material properties, GWP, common uses, renovation relevance and alternatives. ## What the architect validates - Whether the material fits the existing building, detail, durability, moisture and documentation needs. ## Key figures | Metric | Value | | --- | --- | | GWP | 0.85 kg CO₂-eq/kg | | Density | 10–50 kg/m³ | | Expected lifetime | 50+ years | ## Use - Attic insulation - Exterior walls in lightweight construction - Partition walls with acoustic requirements - Ventilation ducts ## Renovation relevance Glass wool is the classic choice for retrofitting insulation in older attics. Easy to blow into attic spaces and install in rafter bays. Inexpensive and effective solution for a homeowner with a limited budget. ## Comparison | Material | GWP | | --- | --- | | Cellulose insulation | 0.12 | | Glass wool | 0.85 | | Mineral wool (stone wool) | 1.05 | | EPS | 3.29 | ## FAQ ### Is glass wool cheaper than rock wool? Typically yes — glass wool is 10–20% cheaper than rock wool for comparable properties. It is slightly more compressible and lighter, but has slightly lower fire safety and sound absorption. ### Can glass wool be used outdoors? Glass wool is not suitable for moisture-exposed structures. It loses insulating capacity when absorbing moisture. For exterior facade insulation, rock wool facade batts approved for the purpose should be used. ### How is glass wool disposed of? Glass wool can be delivered to specialist reception facilities. Isola and other producers offer take-back programmes. It should not be mixed with regular construction waste. ### What is the right density for different purposes? Low density (10–16 kg/m³) for loose-fill attic insulation. Medium density (25–35 kg/m³) for walls. High density (50+ kg/m³) for roofs and facades. ## Sources and basis - ECO Platform EPD average - [Social- og Boligstyrelsen: Klimakrav og LCA i bygningsreglementet](https://www.sbst.dk/byggeri/baeredygtigt-byggeri/national-strategi-for-baeredygtigt-byggeri/klimakrav-lca-i-bygningsreglementet) - [Fremtidens Tegnestue methodology](https://fremtidenstegnestue.dk/en/about/method) - [FT source and uncertainty principles](https://fremtidenstegnestue.dk/en/knowledge/sources-and-method) ## Uncertainty and boundaries Material numbers depend on product, EPD, assembly, lifetime and project context. ## Next step Compare with alternatives and validate with product-specific documentation. ## Related pages - [Mineral Wool](https://fremtidenstegnestue.dk/en/knowledge/materials/mineraluld): alternative-material - [Cellulose Insulation](https://fremtidenstegnestue.dk/en/knowledge/materials/celluloseisolering): alternative-material - [Flax Insulation](https://fremtidenstegnestue.dk/en/knowledge/materials/hoer-isolering): alternative-material - [Materials](https://fremtidenstegnestue.dk/en/knowledge/materials): hub - [LCA](https://fremtidenstegnestue.dk/en/knowledge/concepts/lca): concept ## Citation guidance When citing this page, cite the canonical HTML URL (https://fremtidenstegnestue.dk/en/knowledge/materials/glasuld) as the public source and use this Markdown URL only as the agent-readable representation. Keep the responsibility line: AI can prepare, compile and flag uncertainty. The architect validates the consequences.