Double Reflective (Multifoil) Insulation: What It Is, How It Works and Where to Use It
Why insulation matters now
With energy costs rising, UK households are looking for upgrades that improve comfort without stealing space. Double reflective insulation — often called multifoil — is a slim, high-performance option that helps keep warmth in during winter and limit heat gain in summer, making whole-home efficiency easier to achieve.
What is double reflective insulation?
Double reflective or multifoil insulation is built from multiple layers, including two highly reflective foil faces separated by cores such as bubbles, foam or wadding. The layered build-up is designed to manage heat transfer while keeping the overall thickness low.
How it works
- Radiant: The reflective surfaces bounce a large share of radiant heat back towards its source in winter and away in summer.
- Conductive: Internal layers and trapped air spaces reduce heat flow through the material.
- Convective: The multi-layer structure helps limit air movement which reduces convective losses.
Key benefits
- Strong thermal performance for its thickness — helpful where depth is limited.
- Versatile — suitable for roofs, walls, floors, conservatories, garages and garden rooms.
- Lightweight and flexible — easier to handle for DIY or professional installs.
- Moisture control — foil facings can act as part of a vapour control strategy when joints are sealed correctly.
- Clean install — minimal mess compared with some traditional products.
Good places to use it
- Lofts and pitched roofs — over or under rafters as part of a layered build-up.
- Timber studs and framed walls — internal linings where space is tight.
- Floors over unheated spaces — to reduce heat loss to garages or voids.
- Outbuildings and garden rooms — quick comfort gains in lightweight structures.
- Conservatories and sunrooms — to reduce summer heat gain and winter losses.
Installation tips
- Fix to joists or studs with staples or appropriate fixings, then seal all laps and edges with foil tape to maintain performance.
- Maintain air cavities as specified by the manufacturer on one or both faces, typically around 25 mm, to enable the reflective layers to work effectively.
- Avoid compressing the material which can reduce performance.
- Coordinate with ventilation and vapour control so moisture is managed properly.
- Keep clearances from recessed lights and heat sources as per safety guidance.
Common mistakes to avoid
- Skipping the air gap or sealing — which undermines radiant performance.
- Creating thermal bridges with uninterrupted timber or metal members.
- Using multifoil as a direct substitute where regulations call for a specific U-value without a full build-up calculation.
How multifoil compares
- vs Mineral Wool: Multifoil offers slim build-ups and radiant control, while mineral wool excels at cost-effective thermal and acoustic performance at greater thickness.
- vs PIR boards: PIR delivers high thermal resistance per mm in rigid sheets for flat linings. Multifoil can be easier around irregular shapes and can complement PIR in hybrid systems.
Where to buy
At Buy Insulation you will find a curated range of double reflective (multifoil) insulation rolls plus tapes and accessories to complete the job. Our team can recommend build-ups for roofs, walls and floors based on your project.
Conclusion: a smart, space-saving upgrade
Double reflective insulation is a practical way to boost comfort and efficiency without bulky depths. Specify it correctly, maintain the required air spaces and seal the system well for reliable results — whether you are upgrading a loft, lining a garden room or tackling a full refurb.
