TOP TIPS ON HOW TO INSTALL FOIL FACED INSULATION THE RIGHT WAY*

Foil Faced Insulation has gained significant traction in the UK, thanks to its exceptional ability to reduce heat transfer and boost energy efficiency. Its reflective foil surface is particularly effective at bouncing back radiant heat, making it suitable for a wide range of applications. This feature allows builders and homeowners to achieve better U-values with slimmer profiles—an important benefit in today’s space-conscious construction projects. In a country like England, where the weather can be highly unpredictable and lead to uncomfortable indoor temperatures, foil insulation proves to be a reliable way to maintain thermal comfort.

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In this article, we’ll walk you through the proper installation of Foil Faced Insulation—ideal for DIY enthusiasts looking to handle the job themselves. Here are some practical tips to help you get started.

 TABLE OF CONTENTS

• TOP TIPS ON HOW TO INSTALL FOIL FACED INSULATION THE RIGHT WAY
  
• WHAT IS FOIL FACED INSULATION?
• WHICH WAY DOES FOIL INSULATION GO?
• WHERE TO USE FOIL FACED INSULATION?
• WHAT ARE THE TYPES OF FOIL FACED INSULATION?
• 1.HOW TO INSTALL FOIL BACKED INSULATION IN STUD WALLS?
• 2.HOW TO INSTALL FOIL BACKED INSULATION ON CEILING?
• 3.HOW TO INSTALL FOIL BACKED INSULATION ON CONCRETE WALLS?
• 4.HOW TO INSTALL FOIL BACKED INSULATION ON ROOF?
• 5.HOW TO INSTALL FOIL BACKED INSULATION ON FLOOR?
• 6.HOW TO INSTALL FOIL BACKED INSULATION IN A SHED?
• 7.HOW TO INSTALL FOIL BACKED INSULATION AROUND WINDOWS AND DOORS?
• THERMODYNAMIC vs FOIL FACED INSULATION

WHAT IS FOIL FACED INSULATION?

Foil-faced insulation is a type of thermal insulation that includes a reflective foil layer bonded to one or both sides of the insulation material. This foil acts as a radiant barrier, helping to reflect heat away from the surface rather than allowing it to be absorbed. As a result, it significantly reduces the transfer of radiant heat, enhancing the overall energy efficiency of a building.

The core insulating material—such as mineral wool, rigid foam, or fibreglass—may in some cases be combustible, but the foil facing itself is usually non-combustible. Many foil facings are rated Class 0 in accordance with UK building regulations, which means they exhibit limited combustibility and contribute minimally to fire spread. When correctly installed, this type of insulation can improve both thermal performance and fire resistance.

In addition to its heat-reflective qualities, foil-faced insulation can also act as a vapour control layer, helping to reduce condensation within walls, roofs, and floors. This makes it a popular choice in both residential and commercial construction, particularly in spaces where managing heat gain or loss is crucial—such as lofts, cavity walls, and industrial buildings.

Overall, foil-faced insulation offers a multi-functional solution that enhances thermal comfort, boosts energy efficiency, and adds an extra layer of safety to the building envelope.

Pic. Illustration generated with AI

WHICH WAY DOES FOIL INSULATION GO?

To understand which side the foil should face, it is essential to recall basic laws of physics. These laws state that the flow of energy occurs due to temperature differences between bodies and always moves from a warmer to a colder body. Therefore, warm heated air in a room will always seek to escape towards the cold. To prevent this process, a physical barrier should be placed between these temperatures, typically in the form of insulation.

Unfortunately, insulation itself tends to accumulate heat over time. However, insulation with aluminum foil not only accumulates heat but also reflects the heat source as per below picture.

By placing a barrier between two different temperatures, we prevent heat loss. Additionally, using insulation with aluminum foil reflects the heat back into the room, providing a double benefit.

Therefore, it is crucial to install foil-faced insulation on the correct side. You are free to copy and share the text from this blog, as long as you provide proper credit and a link to the original source-https://insulationgo.co.uk/

When working with foil faced insulation, you should use its advantages accordingly. When installing foil faced insulation, it’s generally most effective to have the foil side facing the area with the greatest temperature difference. This allows the reflective surface to work as intended—reducing radiant heat transfer by reflecting it back toward the heat source. In colder conditions, this often means facing the foil inward to retain heat, while in warmer environments, it might be more beneficial for the foil to face outward, helping to deflect external heat. Correct positioning can significantly improve thermal performance and energy efficiency.

So, any time you use a single side foil insulation, the foil needs to be facing toward the living space. So in a loft the foil faces downward. If you install double faced insulation it doesn't really matter which side is out. Neither side does the same job. Therefore, it is easier to use insulation with foil on both sides.

TIP:Because of the way foil backed insulation works, foil needs a section of air next to the reflective surface to work. This is where the heat goes once it has been reflected back from the insulation surface. Therefore, all types of foil backed insulation reflects radiant heat and works best with an air layer of at least 25mm-50mm

Pic. Illustration generated with AI

WHERE TO USE FOIL FACED INSULATION?

Foil-faced insulation can be used in very specific situations such as:

• Pitched roof – between rafters creating vapour barrier and preventing moisture build up.
• Ceiling - between floor joists where it acts as a sound transmission barrier.
• Hot parts of a house that may become overheated during summers.
• Commercial buildings where foil prevents the spread of flames and inhibits heat and smoke through concealed spaces.
• Government buildings to maintain high performance over the lifetime of the building.
• New build and refurbishment projects.
• Internal partitions, timber and metal studs where excellent sound absorption characteristics are needed.

WHAT ARE THE TYPES OF FOIL FACED INSULATION?

Foil faced insulation comes in many formats such as:

• foil backed fibreglass wool,
• foil backed stone mineral wool 
• foil backed polystyrene (EPS),
• foil backed PIR such a Unilin, Celotex or Kingspan.

HOW TO INSTALL FOIL BACKED INSULATION IN STUD WALLS?

If you are wondering how to install the foil backed insulation on your walls here you have few tips to consider.

• if it is hot outside, the reflective part of your foil insulation must face outside.
• if it is freezing outside, the best orientation of the reflective part is inside. 
• if you press the foil side of the insulation tight up against the wall (foil facing outward), the radiant barrier will not work.
• if you create a gap between the wall and the insulation board (foil facing out) then you will have a radiant barrier. Here, not only is your insulation working, but so is the radiant barrier - you are reducing your conductive and radiative heat loads entering the building. The insulation will keep the heat out on hot days, and keep the heat in on cold days, and the radiant barrier will keep the heat out on hot days.

1. Check the Stud Wall Construction
Ensure the timber studs are dry, sound, and evenly spaced (usually 400 mm or 600 mm centres).

2. Measure and Cut the Insulation Boards
Use a rigid foil-backed board like PIR (e.g., Celotex GA, Kingspan, Unilin).

Measure the cavity between the studs and cut boards to fit snugly between the timber members.

A tight friction fit is ideal, but not so tight that it bows or damages the board.

Tip: Cut with a fine-tooth saw or insulation knife. Score and snap also works for thinner boards.

3. Fit Insulation Between the Studs
Push each cut piece into the space, foil face pointing inward (toward the warm side of the wall).

Boards should sit flush with the front edge of the studs or be slightly recessed if you plan to add a service void later.

Note: Leave no gaps. Use small offcuts or expanding foam to fill any unavoidable gaps around edges.

4. Tape All Joints
Seal all joints between boards with foil insulation tape (e.g., aluminium tape rated for PIR).

This creates a continuous vapour control layer.

If boards don’t sit flush, fill gaps with appropriate foam before taping.

5. Optional: Continuous Layer Over the Studs
For better thermal performance, you can add a second continuous layer of foil-faced insulation over the studs.

This minimises thermal bridging through the timber.

6. Finish the Wall
Fix plasterboard (drywall) over the insulation or battens using drywall screws.

Avoid penetrating the foil-backed insulation with unnecessary screws.

7. Seal Edges and Junctions
Use acrylic sealant or expanding foam at floor, ceiling, and corner junctions to prevent air leaks.

Maintain the vapour barrier continuity across adjoining surfaces (e.g., floors, ceilings, and adjacent walls).

✅ Additional UK Considerations

• Building Regulations: Comply with Part L (thermal performance) and Part C (moisture).
• U-values: Check target U-values for your project (commonly 0.28 W/m²K or better for refurbishments).

HOW TO INSTALL FOIL BACKED INSULATION ON CEILING?

Generally speaking, there are two methods of installing foil backed insulation on ceilings. Regardless of the method, the foil should be placed on the warm side of the room. 
In the first most commonly used method, the foil faced insulation goes between the ceiling joists. It does not take up much space and does not change the height of the ceiling. Nevertheless, the continuity of the insulation itself is interrupted and the aluminium foil does not constitute a barrier in its entirety. Usually this form of installation does not require screws to be used. You are free to copy and share the text from this blog, as long as you provide proper credit and a link to the original source-https://insulationgo.co.uk/

Illustration generated with AI

While the second method is more effective, it is less frequently used. Here, foil backed insulation goes over ceiling joists creating continuous insulation and vapour layer. This method requires long screws to be used. Therefore, holes are created. When laying your foil faced insulation over the joists, it’s best to work at a 90-degree angle to the joists, running in the opposite direction.

HOW TO INSTALL FOIL BACKED INSULATION ON CONCRETE WALLS?

In the UK, a home's concrete walls are in the basement. This creates challenges. Why? Because basement walls are almost always below ground level. When heat or cold comes in contact with concrete it passes right through with almost no resistance. 
Typical insulation works in a basement but you have to use a good vapour barrier along with it. This is where foil faced insulation takes its place.

Using foil-faced rigid foam boards is a practical solution for insulating concrete walls, especially when a vapour barrier between the concrete and the interior is desirable. Foil-faced EPS or PIR boards work particularly well in this context.

Concrete walls in basements are constantly exposed to ground moisture, so there’s no benefit in allowing them to dry toward the interior—it’s not achievable, as the moisture is continuously replenished from the surrounding soil. Instead, it’s more effective to contain the moisture within the concrete, which is not harmful to the material and can even contribute to its durability.

Before proceeding with basement insulation, it’s important that the building is free of water infiltration issues. If any are present, they should be resolved first. When installing foil-backed insulation boards like EPS, mechanical fasteners should be avoided, as they can compromise the foil layer. A compatible adhesive is preferred, as it preserves the integrity of the vapour barrier.

Boards should be fitted tightly together, and using the longest possible lengths reduces the number of joints. All joints between foil-faced boards should be sealed with approved aluminium tape. If the seams are properly taped and the floor edge is sealed with caulk, moist indoor air is prevented from reaching the cold concrete surface.

HOW TO INSTALL FOIL BACKED INSULATION ON ROOF?

For insulating a warm roof in particular, foil backed insulation is a great choice. Pitched roof insulation installation is very similar to the ceiling. While insulating the ceiling, foil backed insulation is usually placed between the floor joists or over the joints, in a pitched roof, these two methods are used. 

Illustration generated with AI

Contact us to discuss your requirements of glass wool with aluminium foil. Our experienced sales team can help you identify the options that best suit your needs.

The easiest way to insulate the roof with foil faced insulation is between and beneath the rafters as you don’t have to worry about the accuracy of the cuts. A suitable material for roof insulation is rigid foam board, such as Unilin or Celotex.

However, this may not be an option if the space is tight because it will eat into the available headroom.

Using PIR insulation with foil on both sides you won’t have to worry about its direction. Whichever site you install, it will always be fine.

For example, selecting insulation with foil on both sides means the wall build-up ends up with two reflective vapour-resistant layers. For your own comfort and safety, try to avoid installing it in the middle of the summer, when your loft is at its hottest.

HOW TO INSTALL FOIL BACKED INSULATION ON FLOOR?

To achieve maximum floor thermal and vapour performance and to ensure fast and simple installation of foil faced rigid insulation panels for retrofit or new underfloor systems, it is recommended to do the following.

• measure distance between floor joists,
• cut PIR foil faced board to size,
• install foil faced board between floor joists,
• use aluminium tape to seal the but joins between the rigid boards and any other minor gaps,
• continue along cutting around any services as required,
• fill the holes with expanding foam.

Illustration generated with AI

HOW TO INSTALL FOIL BACKED INSULATION IN A SHED?

Insulating a shed isn’t a must-do project, however, it can make it a more pleasant place for you. Moreover, an insulated shed might prove a better environment for the items you store inside it. 
Insulating your shed can be done cheaply with a few quick hacks. To achieve best thermal performance and to ensure a fast installation of foil faced rigid insulation board to a shed it is recommended:

• to get full access to the shed remove all of its contents,
• rigid insulation panel such as PIR should be installed between the wall girts and to the underside of the roof battens,
• fasten the foil faced insulation panel to the roof battens with screws using approx. 6 per m2,
• cut the foil backed boards to fit between the floor joists, laying them flush with the top of the joists, next replace the floor,
• use aluminium tape to seal the but joins between the rigid boards,
• if your shed is made of wood, you can finish the walls with plywood.

You can use stone wool foil faced insulation for shed walls if you want the very best sound insulation for yours. Use slabs with a vapour barrier to control moisture. To find out  how to insulate a shed click here

 

HOW TO INSTALL FOIL BACKED INSULATION AROUND WINDOWS AND DOORS?

If you are placing the foil backed insulation in a window, face the radiant barrier outward. Otherwise, the heat that enters through the window will serve to heat the insulation board, and the board will in turn, serve to heat the room like a heating element in the oven. The radiant barrier facing outward will prevent this to a certain extent. 

THERMODYNAMIC vs FOIL FACED INSULATION

Thermodynamic fact of life - if you put any two objects with different temperatures together, then heat transfer will cause them to reach the same temperature.
Foil faced insulation works on "Thermos" principles.
For instance, if you want to keep your hot tea as long as possible inside Thermos - that is, if you want to slow down the natural heat transfer process as much as you can - you have to slow down the 3 processes that cause heat transfer. In other words:

• Conduction 
• Radiation
• Convection 

To build a good thermos (in this case - insulation), what you want to do is reduce these three heat transfer phenomena as much as possible. So, the foil goes on the warm side to reflect the heat back. If it is on the cold side, the smaller amount of low temperature radiation will not go directly back into the room but into the insulation where it will be absorbed. 

CONCLUSION

In summary, it is crucial to remember that foil-faced insulation is one of the most modern forms of home insulation, serving dual functions. Its insulating core protects against cold, while its aluminum foil reflects heat back to its source. This ensures that the insulation is always effective and fulfills its purpose. The aluminum foil on the upper part of the insulation can, under specific conditions, act as a Vapor Control Layer (VCL) and provide additional protection against rodents, for whom the foil may be irritating.

Foil faced insulation is also invaluable when it comes to fire performance. It is entirely non-combustible, and the aluminum foil further safeguards our home.

Installing foil faced insulation is not particularly complicated; one just needs to keep in mind the basic principles of physics and place the foil on the side where heat or cold retention is desired.

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Insulation is a vital component of any building project, as it can improve the thermal performance, acoustic comfort, fire safety, and sustainability of your property. However, not all insulation materials are created equal, and choosing the right one can be a challenge.

In this article, we will compare two of the most popular types of insulation: glasswool and mineral wool. We will look at their properties, advantages, disadvantages, and applications, and help you decide which one is best for your needs.

What are Glasswool and Mineral Wool?

Glasswool and mineral wool are both made from mineral fibres that are spun into wool-like strands. They are also known as synthetic vitreous fibres (SVF) or man-made mineral fibres (MMMF). They are widely used as insulation materials because they have low thermal conductivity, high sound absorption, and excellent fire resistance.

• Glasswool is made from melted glass that is spun into fine fibres. It is also called fibreglass or glass fibre. It can be found in batts, rolls, loose-fill, or boards.
• Mineral wool is made from melted rock or slag that is spun into coarse fibres. It is also called rockwool or stone wool. It can be found in batts, rolls, or slabs.

Buy Mineral Wool Insulation

How do Glasswool and Mineral Wool Compare?

Glasswool and mineral wool have many similarities, but also some differences that affect their performance and suitability for different applications. Here are some of the main factors to consider when comparing them:

• Thermal insulation: Both glass wool and mineral wool have similar R-values (a measure of thermal resistance) of around 0.57 per inch of thickness. This means they can effectively prevent heat loss or gain in your building.
• Acoustic insulation: Mineral wool has a higher density than glass wool, which makes it more effective at absorbing sound waves and reducing noise transmission. Mineral wool is therefore a better choice for soundproofing walls, ceilings, floors, or roofs.
• Fire resistance: Both glasswool and mineral wool are non-combustible and can withstand high temperatures without melting or burning. However, mineral wool has a higher melting point than glasswool (over °C vs 700°C), which gives it an edge in fire protection.
• Moisture resistance: Mineral wool is more resistant to water than glasswool, as it does not absorb moisture or support fungal growth. Glasswool can get damp and lose its insulating properties if exposed to water or humidity. Mineral wool is therefore more suitable for wet or humid environments.
• Ease of installation: Mineral wool is easier to handle than glasswool, as it is stiffer and easier to cut and fit into place1. Glasswool is softer and more flexible, which makes it harder to install in tight spaces. However, glasswool is lighter than mineral wool, which makes it easier to transport and lift.
• Sustainability: Both glasswool and mineral wool are made from recycled materials, such as glass, sand, stone, or slag3. They are also energy-efficient, as they save more energy than they consume during their production and use. However, glasswool has a higher recycled content than mineral wool (up to 86% vs 70%), which makes it more environmentally friendly.

Tabular Comparison for Glasswool and Mineral Wool

This table provides a basic comparison of the properties of Glasswool and Mineral Wool. Glass wool is easier to handle and more affordable, while Mineral Wool generally offers better moisture resistance and higher R-values. The choice between them depends on specific project requirements and priorities.

Buy Glasswool Insulation

Choosing the Right Insulation for Your Project

When it comes to insulating your building or space, two popular options to consider are glass wool and mineral wool insulation. Here, we address some frequently asked questions to help you make an informed decision:

Thermal Performance:

Both glass wool and mineral wool insulation offer excellent thermal performance, but mineral wool has higher thermal resistance (R-value), making it more effective at reducing heat transfer and maintaining comfortable indoor temperatures.

Soundproofing:

Both types are effective for soundproofing, with mineral wool having an advantage due to its density and superior sound insulation capabilities.

Combining Insulation:

You can use glass wool and mineral wool together to enhance thermal and acoustic performance, ensuring proper installation and adherence to building codes.

Key Differences:

Glass wool is made from glass fibres, while mineral wool comes from rock or stone fibres. The choice between them depends on your project's specific needs, with glass wool excelling in thermal performance and mineral wool in fire protection.

Glass Wool for Sound Insulation:

Glass wool is frequently used for sound insulation, thanks to its outstanding sound absorption properties.

R-Value:

The R-value of glass wool varies by product and thickness, but it typically offers superior thermal insulation.

Alternative Insulation Materials:

Other options include fibreglass insulation boards, cellulose insulation, spray foam, and polyurethane foam insulation, chosen based on your project's requirements and budget.

Weight and Roll Insulation:

Glass wool is lighter than mineral wool, making it easier to handle and install. It's available in roll form, providing a cost-effective and efficient insulation solution.

Fire Protection:

Mineral wool is the preferred choice for fire protection, as it is non-combustible and can withstand high temperatures without releasing toxic fumes.

Which One Should You Choose?

The choice between glasswool and mineral wool depends on your specific project requirements, budget, and preferences. Here are some general guidelines to help you decide:

• Choose glasswool if you want a lighter, cheaper, and more sustainable insulation material that can provide good thermal insulation for your building.
• Choose mineral wool if you want a denser, stronger, and more durable insulation material that can provide better acoustic insulation and fire protection for your building.

Difference Between Knauf Earthwool DriTherm Cavity Slab 37 and Rockwool RWA45 Slab

Feature Knauf Earthwool DriTherm Cavity Slab 37 Rockwool RWA45 Slab Material Stone mineral wool Stone mineral wool Application Cavity walls Walls, floors and roofs Thermal conductivity 0.037 W/mK 0.035 W/mK Fire rating Euroclass A1 Euroclass A1 Sound absorption Good Excellent Water repellence Yes No Price (per pack) £19.20 £19.20 R-value (for 100 mm thickness) 2.70 m2K/W 2.86 m2K/W

The main differences between the two products are:

• Knauf Earthwool DriTherm Cavity Slab 37 is designed specifically for cavity walls, while the Rockwool RWA45 Slab is more versatile and can be used for walls, floors and roofs.
• Rockwool RWA45 Slab has a lower thermal conductivity and a higher R-value than the Knauf Earthwool DriTherm Cavity Slab 37, which means it can provide more thermal insulation for the same thickness.
• Rockwool RWA45 Slab has a higher sound absorption coefficient than the Knauf Earthwool DriTherm Cavity Slab 37, which means it can reduce more noise and improve the acoustic comfort of the building.
• Knauf Earthwool DriTherm Cavity Slab 37 has a water repellent additive, while the Rockwool RWA45 Slab does not, which means it can resist moisture and prevent dampness and mould growth in the cavity.

These are some of the key differences between the two products that you should consider when choosing an insulation product. 
 

Where Can You Buy Glasswool and Mineral Wool?

If you are looking for high-quality glass wool or mineral wool products for your insulation project, you can find them at Buy Insulation Online. We are a leading online supplier of insulation materials in the UK, offering a wide range of products at competitive prices.

Whether you need batts, rolls, slabs, boards, or loose-fill insulation, we have it all in stock and ready to deliver to your doorstep. You can browse our website Buy Insulation Online to find the best insulation products for your needs.

Frequently Asked Questions

Q: What is the difference between glass wool and mineral wool insulation?

A: Glass wool and mineral wool insulation are two types of thermal insulation materials. The main difference lies in the composition of the fibers used. Glass wool insulation is made from glass while mineral wool insulation is made from rock minerals or slag.

Q: Which is better for insulation, glass wool or mineral wool?

A: The choice between glass wool and mineral wool insulation depends on the specific requirements of your project. Glass wool insulation has better sound insulation properties and is lighter than mineral wool. On the other hand, mineral wool insulation has higher thermal resistance and is denser than glass wool.

Q: What are the advantages of glass wool insulation?

A: Glass wool insulation is known for its excellent sound insulation properties. It is also lightweight and easy to install. Glass wool insulation is made from recycled glass, making it an environmentally friendly choice. Additionally, it has good fire resistance and does not promote the growth of mold or mildew.

Q: What are the advantages of mineral wool insulation?

A: Mineral wool insulation has excellent thermal resistance properties, making it highly effective in reducing heat transfer. It is also denser than glass wool, providing better sound insulation. Mineral wool insulation is made from rock minerals or slag, which makes it naturally fire-resistant. It is also resistant to moisture, mold, and pests.

Q: Is fiberglass insulation the same as glass wool insulation?

A: Yes, fiberglass insulation is another term for glass wool insulation. It is made from fine fibers of glass and is commonly used for thermal and acoustic insulation purposes.

Q: How is glass wool insulation made?

A: Glass wool insulation is made by melting glass and spinning it into fibres. The fibres are then processed and bonded together to form the insulation material. The manufacturing process involves the use of high temperatures and binders to ensure the fibres are properly bonded.

Q: How is mineral wool insulation made?

A: Mineral wool insulation is made by melting rock minerals or slag and spinning them into fibres. The fibres are then processed and formed into insulation products, such as boards or rolls. The manufacturing process may also involve the addition of binders or coatings for improved performance.

Buy Mineral Wool Insulation   

Conclusion

Glasswool and mineral wool are both excellent insulation materials that can improve the comfort and efficiency of your building. However, they have different properties and advantages that make them more suitable for different applications.

By comparing their thermal insulation, acoustic insulation, fire resistance, moisture resistance, ease of installation, and sustainability, you can choose the best insulation material for your project. If you need any help or advice, feel free to contact us at Buy Insulation Online. We are happy to assist you with your insulation needs.

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