Fibreglass batt insulation is made from spun glass fibres formed into dense, flexible mats. These mats are produced by melting raw materials such as silica sand and recycled glass at high temperatures, then extruding and attenuating the molten glass into fibres.
This type of insulation provides excellent thermal resistance, with K-values typically ranging from 0.035 to 0.043 W/m·K, depending on thickness and density. To ensure maximum effectiveness, it must be installed with a proper fit and sealed carefully to prevent gaps or compression, which can reduce its insulating performance.
Following proper installation practices will help optimise the thermal efficiency of your fibreglass batt insulation and contribute to a well-insulated, energy-efficient building.
Manufacturing and Material Composition
The production of fiberglass batt insulation begins with the selection of raw materials such as silica sand and recycled glass, which are carefully combined with minor ingredients including limestone, soda ash, and feldspar. These materials are mixed using a dry blending process to ensure a uniform distribution before they’re subjected to melting. The blend of raw materials also influences the specific properties of the final product, such as thermal resistance and strength. The mixture is then heated in a high-temperature furnace, reaching temperatures of around 1,300°C (2,372°F). This process transforms the raw materials into molten glass with consistent properties necessary for insulation manufacturing.
Once molten, the glass is spun through a series of tiny orifices using a rotary technique. This creates fine glass fibres that are attenuated by hot air streams, forming the fundamental component of the insulation product.
During fibre formation, binders such as phenolic, acrylic, or formaldehyde-free resins are applied to coat the fibres, which enhances cohesion, stability, and durability.
The coated fibres are arranged into uniform mats using specialised machinery, then cut into specified sizes suitable for construction applications.
These mats are subsequently heat-set to stabilise their structure, ensuring they retain their shape and insulating properties over time.
The finished fiberglass batt insulation is lightweight, versatile, and offers effective thermal performance, making it a popular choice for thermal and acoustic insulation in UK buildings.
Thermal Performance and R-Values
The thermal performance of fibreglass batts is primarily characterised by their K-value, which measures their resistance to heat flow. Typically, the K-value for fibreglass batts ranges from approximately 0.030 to 0.035 W/m·K, depending on the product type and density. Higher density batts deliver greater thermal resistance in thinner profiles, as denser materials better trap air by reducing convection. This means they can provide improved thermal performance even with a reduced thickness. Proper installation is essential to maintain the rated thermal performance. Compression or gaps within the batt can significantly diminish effectiveness, sometimes by up to 50%. Ensuring that batts fit snugly within wall cavities without gaps or compression is crucial for optimal insulation. In typical UK residential applications, fibreglass batts offer thermal transmittance values (U-values) that vary between approximately 0.20 and 0.30 W/m²·K, suitable for standard walls and roof spaces. While fibreglass batts offer moderate thermal performance, alternative insulation materials such as foam or mineral wool may provide higher thermal resistance per unit thickness, which can be beneficial in demanding climates or for achieving stricter energy efficiency standards. Additionally, air movement within the cavity can reduce the insulation’s effectiveness if not properly sealed or if gaps are present.
Installation Tips and Best Practices
Proper Installation of Fiberglass Batts Insulation: Tips and Best Practices
Installing fiberglass batt insulation correctly is essential to maximise its effectiveness and improve your home’s energy efficiency. Attention to detail during measurement, fitting, and sealing can prevent cold spots and air leaks, ensuring a warmer, more comfortable living environment.
Measurement and Cutting
Begin by precisely measuring the dimensions of the space to be insulated. Add an extra 1–2 centimetres to each measurement to allow for a snug fit without excessive compression.
When cutting the batts, utilise a sharp utility knife and a straight edge to achieve clean, accurate cuts. This precision is especially important when working around obstacles such as electrical sockets, pipes, or structural elements.
Fitting and Positioning
Gently push the batt into the cavity, ensuring it fills the space entirely without distorting or compressing the fibre. Avoid forcing the insulation too tightly, as compression can reduce its insulation performance.
For irregularly shaped spaces or awkward areas, carefully trim the batts to fit, avoiding gaps or voids that could lead to heat loss.
Sealing Gaps and Edges
To prevent drafts and minimise air infiltration, seal all gaps around window and door frames, as well as between the insulation and the structural framing.
Use suitable products such as sealant or foam to fill larger crevices. For smaller gaps, scraps of insulation can be gently tucked into the space.
Be mindful to keep the insulation flat and uncompressed, maintaining its natural loft and insulating properties.
Additional Tips
- When working around electrical boxes and pipes, make precise cuts to accommodate these features without leaving gaps.
- Avoid overcompression of the batts, as this can significantly diminish their thermal performance.
- Properly install vapour barriers (if used) according to manufacturer instructions, ensuring they’re fitted smoothly with no tears or gaps.
- Maintain good ventilation during installation to prevent moisture build-up, which can compromise the insulation’s effectiveness.
Final Checks
Once installed, double-check all areas for gaps, compressed sections, or areas that may have been missed.
Improve insulation continuity by filling small spaces with bits of scrap insulation and sealing larger ones with appropriate sealants.
Conclusion
Fibreglass batt insulation provides an effective and widely used solution for thermal regulation in buildings thanks to its high thermal resistance and affordability. Ensuring proper manufacturing is essential to achieve consistent quality, while correct installation—following recommended practices—maximises performance and safety.
Individuals should handle materials carefully, ensuring they are fitted properly and avoiding compressing the insulation, which can reduce its insulating properties. Adhering to these best practices guarantees optimal thermal efficiency, energy savings, and long-term durability, making fibreglass batt insulation a dependable choice for a variety of construction projects across the UK.