75mm Insulation

75mm insulation boards, rolls, and slabs are exactly 75mm thick. That depth is measured from one face to the other. This makes it easier to plan installation within joists, studwork, and other cavities.

75mm insulation thickness is common in floors, walls, and partitions where space may be limited or where a bigger board would project beyond the available build-up.

What is 75mm Insulation?

75mm thick insulation is any insulating material, including foam boards, mineral wool rolls, and rigid slabs, cut to a thickness of 75mm. All 75mm insulation materials limit heat transfer through the building fabric.

75mm insulation offers measurable thermal resistance when fitted properly. Some materials have lower thermal conductivity than others, which affects the overall R-value. This means the products resist heat more effectively per millimetre. It is why some 75mm PIR boards can perform nearly as well as thicker, lower-performing materials.

What is 75mm Thick Insulation Used For?

Here is how 75mm insulating products are used:

• Floors: Fit between joists to minimise heat loss underneath fitted flooring, or to help meet U-value targets in solid floors. PIR boards often perform best thermally in this application, while EPS or XPS may be preferred where compressive strength is more critical.
• Walls: Installed between timber or metal studs and in cavity walls. Both rigid boards and wool slabs can be used here.
• Partitions (internal walls and floors): Mineral wool slabs and rolls are effective in reducing sound travel and thermal transfer.
• Roofs/lofts: Used in cold roofs or between rafters where installing deeper insulation is impractical.

Types of Insulation in 75mm Thickness

Common types of 75mm thick insulation include:

Rigid PIR Boards

Firm, foam panels with foil backing. At insulation 75mm thick, they offer high thermal resistance in a relatively shallow layer.

PIR panels pack a lot of insulating power into that 75mm thickness without compressing. The foil facings contribute to thermal performance when installed with appropriate air spaces.

75mm Expanded Polystyrene (EPS)

EPS is strong and can support a considerable load without crushing. As a result, 75mm EPS is commonly used in floors, ground slabs, and flat roof systems where insulation must carry the weight of screeds or finishes.

Also ideal for cavity walls and external wall insulation systems, and popular for standard residential and commercial builds where cost control is a priority.

75mm Phenolic Foam Insulation

75mm boards contain extremely small cells packed tightly together. Because of this structure, the material has very low conductivity.

Phenolic insulation also has good fire behaviour compared with many other rigid foams. It tends to char rather than melt quickly, which helps slow fire spread when used within a tested system.

Delivers strong thermal protection for long service periods without sagging or compressing.

75mm Glass Mineral Wool Rolls

These are soft, fibrous rolls that friction fit between joists or studs. The material is cut to size and friction-fitted. Rolls absorb noise and are noncombustible (Euroclass A1).

They are useful in internal partition walls or floors where sound control is as important as warmth.

75mm Rock Mineral Wool Slabs

These slabs are denser than glass wool.

They are classified A1 (noncombustible) for fire performance and are good at absorbing sound. They also hold their shape once fitted.

Commonly specified for separating walls, floors, and ceilings.

FAQ

Where to buy 75mm thick insulation

You can buy 75mm insulation thickness products online from Insulation Wholesale, a UK specialist insulation store. We stock PIR boards, glass wool, mineral slabs, and more at wholesale prices, with fast delivery across the UK. Contact us for competitive pricing with trade deals, fast quotes, and credit options.

How to cut 75mm insulation

Cutting methods depend on material type:

For PIR boards: 

1. Draw a line along the area you want to cut.
2. Score repeatedly with a utility knife until the tool passes through the material. Or cut with a fine saw.
3. Go slow to avoid chipping the edges.

For mineral wool rolls/slabs:

1. Place a straight edge where you are cutting.
2. Push straight through the wool using a long-bladed knife or serrated insulation knife.

Wear goggles and a dust mask, as airborne fibres can irritate.

How to fix 75mm insulation

Between timber studs or floor joists: 

1. Insert the insulation gently until it friction-fits between joists or studs. It should stay up without gaps.
2. Use adhesive or fixings if needed to fasten PIR sheets – board adhesive, insulation plugs, or screws with washers.
3. Work from the bottom up, where applicable, so that each layer supports the one above.

Against walls: 

1. PIR boards can be glued directly to the substrate (render, blockwork) using the appropriate adhesive.
2. Use mechanical fixings if required by the manufacturer or building control.

To seal joints: 

Butt insulation edges tightly and seal gaps with insulation tape or foam to reduce draughts and heat leaks.