Insulation 101: The Ultimate Guide to Glass Wool

October 14, 2022

With energy prices soaring as we speak, installing insulation is one of the most cost-effective improvements for any home. Initial costs are redeemed quickly, in most cases within a couple of years, but the benefits last a lifetime.

Homeowners can insulate different parts of their homes depending on the type and previous work. Though you may have missed the Energy Company Obligation, ceasing in March of this year, lower energy bills are possible with some form of insulation lining floors, walls, and roofs. In addition, you'll be reducing your home's carbon footprint and eligible for a higher EPC rating, something to consider if you're selling or renting out the property.

There are various materials and insulation solutions for homes. If your property has wall cavities, using simple and low-cost insulation materials like glass wool will see you retain more heat inside in the colder months. You can also opt to spend a little more and have rigid insulation foam boards installed or choose to have walls filled with expanding spray foam.

The same applies to lofts and roofs. Budget-conscious buyers that choose glass wool still get all the benefits of more expensive foam boards, such as high thermal efficiency, soundproofing and flame, water, and corrosion resistance without the high costs. If you're looking for value and more warmth in the winter, glass wool is a good place to start.

What Is Glass Wool?

Glass wool is a durable and resistant insulative material made of silica sand, recycled glass and binders, spun into a texture similar to wool at high heat. It's often sold in blanket form, either as pre-cut panels or batts in standardised sizes or as longer rolls cut to size.

Without the binding agents, the material is also available as a loose-fill option, blown into roofs and lofts. The dense glass fibres are filled with air pockets and work to trap air and stop airflow. As a result, they prevent heat from escaping.

How Is It Made?

This inexpensive insulative material is made from sand, limestone and sodium carbonate (soda ash), and a high proportion (up to 70%) of recycled glass. These are then melted at high temperatures (approximately 1500 degrees Celsius), spun into fibres and conditioned with resins.

The product is sprayed with binders during the spinning stage, giving the wool its structural stability. The final product is left to cool and harden, then can be cut into rolls or batts.

Benefits of Glass Wool

There are at least half a dozen reasons to choose glass wool as the insulation material for your next home improvement project.

Thermal Insulation and R values

These are the rating systems used to determine the effectiveness of insulation materials. Usually, the higher the number, the better the materials retain heat in colder months and keep areas cool during the summer. R values are impacted by various factors, like the materials and additives used, the production, process, and the thickness or density of the final product.

There are three values to look for here:

  1. Up R-values - the effectiveness of keeping the heat in
  2. Down R-values - how materials keep heat out during warmer days
  3. Total R-value - an average of both and the numbers stated on spec sheets.

For glass wool, numbers range anywhere between 1.2 to 7. How materials are installed and in what thickness will determine the thermal performance of glass wool. The figures generally round out to R-values of 2.7 to 3, meaning it's in line with other insulative products, considering its low cost.

Sound Insulation

While all variants have some form of sound insulation, with the glass fibres absorbing sound waves and preventing transmission, specially formulated Acoustic Partition Rolls, or APR, perform best in this respect. They come in a different colour to be easily recognisable (often golden).

Although, they may have lower R-values and thermal efficiency than standard batts and rolls. APR is effectively used in sound deadening or to isolate particular rooms, for instance, studios, from their surroundings.

Durable and Flexible

Glass wool won't sag, deform or rot over the long run and provides structural support to walls and lofts with its high compressive and tensile strength. In addition, with appropriate vapour barriers, it also resists moisture. It's non-corrosive in walls with steel elements and doesn't attract vermin, bacteria, or fungi. Product life is more than 25 years. Furthermore, its flexibility allows it to conform easily to any given area.

Flame-retardant and Fire-resistant

Although materials like mineral wool may fare better, glass wool is nevertheless rated as a non-combustible product (A1 rating) according to European and British Building Standards and remains intact even when faced with heat as high as 250 degrees and has a very high melting temperature of over 700 degrees. It is non-flammable and has no toxic substances to cause worry.

Recyclable and Sustainable

The product is made of almost 80 per cent recyclable materials and is internationally certified as a green building material, achieving an A+ rating. It contains no harmful substances like CFCs. There's also less waste in production.

Low Cost and Easy to Install

Glass wool batts and rolls are some of the cheapest insulation materials sold. Batts are supplied in standard sizes to fit cavity walls or lofts and are easily installed even as a DIY job. The same goes for rolls, the only difference being the cutting to the appropriate lengths. Even larger rolls are lightweight and easy to manage.

Where Is It Used?

In short, it's applied in loft, roof, and ceiling applications that need a lightweight, thermally efficient insulative material, either on its own or with aluminium foils serving as moisture barriers. Loft rolls come in different lengths and thicknesses. When used with partition and cavity walls, either in timber frame or steel, batts are shorter and can be up to 150mm thick. APR or acoustic glass wool is optioned in still thinner (25 to 100mm) and smaller rolls,

How Does It Compare to Other Insulation Products?

Regarding the cost, favourably. Mineral wool has slightly better thermal performance and water resistance and can stand higher temperatures. However, it's also more expensive when insulating larger areas.

Foam boards are another option. They have almost double the R-values, making them more suitable for extremely cold places. The fact that they hold up against water and fire better and their higher density means they offer more support to existing structural elements.

Glass wool has the advantage of simple installation, being lightweight and with decent thermal properties, and can be used in conjunction with other insulative products to keep in even more heat. When used on its own, it needs to be sourced in thicker batts or rolls to achieve the same results. This won't be a deciding factor in most loft or cavity wall applications, with plenty of space to spare.

As prices go, glass wool batts and rolls come roughly three times cheaper than boards covering the same area and 15-20 per cent cheaper than comparable mineral wool rolls.


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