What is the difference between foil quilt and multifoil loft insulation?

Foil quilt and multifoil insulation are related terms, but they do not describe exactly the same product. Foil quilt usually refers to a flexible blanket, while multifoil describes a layered reflective insulation design. The correct comparison depends on the product’s tested construction, declared thermal performance and intended installation position.

Foil quilt commonly contains one or more reflective foil faces with a soft insulating core. The core may include wadding, foam or another flexible material. It is supplied in rolls and can be fitted around roof timbers, across loft surfaces or in other areas stated by the manufacturer.

Multifoil insulation normally contains several reflective layers separated by low-conductivity materials. These layers can include wadding, foam, mesh or trapped air spaces. The reflective surfaces reduce radiant heat transfer when the adjacent air spaces are installed as specified.

The names can overlap in product descriptions. Some multifoil products are quilted and flexible, so a product may be described as both foil quilt and multifoil. The name alone does not confirm how the insulation performs.

• Construction: foil quilt is often described by its blanket-like form, while multifoil is described by its number and arrangement of reflective and separating layers.
• Thickness: products vary considerably, so thickness should not be used alone to compare thermal performance.
• Installation: some products need clear air spaces beside reflective faces, while others have different requirements. Follow the manufacturer’s installation specification.
• Performance: compare declared thermal values and test information for the complete installed build-up, not just the insulation roll.
• Handling: both types are generally flexible compared with rigid boards, but cutting, joining and fixing still need careful planning.

A foil quilt may suit a loft where flexible material needs to fit between or around roof timbers. A multifoil product may suit a build-up where several reflective layers provide the required performance within limited space. Neither description is enough to confirm suitability for every loft.

Loft construction affects the choice. A pitched roof, loft floor, dormer cheek or eaves area may each require a different insulation arrangement. Existing insulation, ventilation routes, electrical cables and roof coverings also need consideration.

Reflective insulation only performs as tested when the specified air spaces, overlaps, joints and fixings are maintained. Compressing a product, covering a reflective face incorrectly or closing ventilation paths can change the installed result.

For that reason, compare the following information before choosing between foil quilt and multifoil:

• the manufacturer’s declared thermal performance;
• the tested thickness and complete build-up;
• the required air spaces and ventilation arrangements;
• the approved fixing method and treatment of joints;
• the product’s reaction to fire information;
• compatibility with existing insulation and the loft structure;
• whether the product is intended for a roof, loft floor or another location.

Foil quilt or multifoil should not be selected solely because it appears thinner or easier to handle. A thinner product may need a carefully defined build-up to achieve its declared performance, while a thicker product may affect available headroom or access.

Loftopia assesses the existing loft before recommending insulation work. We consider the insulation already present, the roof construction, ventilation and any planned raised flooring. We can also explain how insulation work relates to loft access and storage arrangements.

The practical difference is therefore the product design and tested installation, rather than the label alone. Check the technical specification, then match the insulation to the loft’s construction and the required installation method.