Most UK lofts have the same insulation they had in 1995. Maybe earlier. Roll out the hatch, pull the boards back, and you will almost always find a 50mm to 100mm bed of yellow or pink fibre, partly flattened, partly slumped against the eaves, with the outlines of footprints in it where someone once went up to check the water tank.
It is doing some of the job. It is not doing all of it. And the longer it sits there, the less of the job it is doing.
What is actually in your loft right now
Almost certainly mineral wool. Sometimes called glass fibre, glass wool, or rock wool depending on the manufacturer. It is the standard insulation that has been fitted in UK homes for the past forty years, and it is the material every supplier-driven retrofit scheme defaults to because it is cheap, BBA-certified, and easy to install. It also has four genuine problems that almost no installer will mention while they are quoting.
The four real problems with mineral wool
- Compaction. Mineral wool is fluffy when it goes in and structured when it comes out of the bag. Sit in a loft for twenty or thirty years and it compresses under its own weight. The insulation value is in the trapped air between the fibres; squash those out, and the R-value falls with them. Most lofts we open up are running at about half the thermal performance the original install claimed.
- Formaldehyde binders. The glass or rock fibres themselves do not stick together. A binder — usually formaldehyde-based — is what holds the wool in a coherent batt. That binder slowly releases formaldehyde into the air inside the house, particularly in older installs where the binder has started to break down.
- Sharp fibres. The reason every installer wears a full mask, gloves, and overalls when fitting mineral wool is that the fibres irritate the skin, the eyes, and the lungs on contact. The fibres do not become safe once installed; they become contained. But every time you go into the loft for the suitcases, every time you replace a downlight, every time the loft hatch gets disturbed, fibres come down into the house.
- Moisture. Mineral wool absorbs water. When it gets wet — a slipped tile, a small roof leak, a burst pipe overhead — it cannot dry out. The absorbed water destroys the R-value, holds against the timber, and starts the mould cycle. By the time you see anything from inside the house, the loft is already compromised.
On top of the four physical problems, there is a financial one. Mineral wool that has compacted by half is delivering half its rated thermal performance. The bill it was supposed to cut is creeping back up year on year, and the homeowner has no way of telling without lifting a section of the loft and measuring the depth.
“Properties with spray foam insulation may warrant a valuation reduction of 15 to 20 per cent.”
— Royal Institution of Chartered Surveyors guidance, 2025
The valuation framework that flags spray foam does not currently apply the same scoring to mineral wool. But the broader point holds: insulation that is below specification, suspected to be contaminated, or suffering moisture damage will be noted on a Home Buyers Report and may be reflected in the offer the buyer puts forward. The cost of mineral-wool degradation is paid at sale, not at install.
How multifoil solves all four
Multifoil is a different category of insulation entirely. It is not a fluffy mat. It is a thin, layered, reflective laminate — more than 20 layers of aluminium foil and engineered foam, 40mm or 80mm thick depending on the application, fixed on battens between or under the rafters.
It works by reflecting radiant heat back into the room rather than just slowing conduction the way mineral wool does. Two-thirds of the heat lost from a typical UK ceiling is radiant infrared; multifoil reflects 95% or more of it back. The conducted-heat fraction goes through the air gaps trapped between the foil layers, which are themselves doing a job. The net effect is that 40mm or 80mm of multifoil outperforms 200mm of mineral wool in most installations.
And because it is foil and foam, not glass fibres in a binder, none of the four mineral-wool problems apply. It does not compact. It uses no formaldehyde binder. There are no sharp fibres to irritate skin or lungs. And if a roof leak develops, the foil sheds the water rather than absorbing it — the loft can dry, the timbers stay sound, the install is salvageable.
When mineral wool is still the right answer
There are cases. A new-build loft with deep rafters, fully ventilated, where the owner intends to use the loft for storage and is happy to walk on the boards while wearing a mask. A cold-roof retrofit where the budget is genuinely the constraint and the customer accepts the trade-offs. A specific PAS 2035 specification that calls for mineral wool by name. We still fit mineral wool in those cases. We just do not fit it as the default.
For everything else — which is most of the homes we survey — multifoil is what the survey recommends, and what we install.
Frequently asked questions
- Is mineral wool dangerous to live with once it is installed?
- Once it is in place and sealed, the day-to-day risk is low. The fibres themselves are contained behind ceiling boards and loft hatches. The formaldehyde release continues at a low level but is generally below health-significant thresholds. The risk profile rises every time the loft is disturbed.
- Will multifoil work in a converted loft?
- Yes — this is one of its strongest applications. Multifoil between the rafters keeps the headroom in a converted loft that mineral wool would steal. It is the standard answer for room-in-roof conversions.
- How long does multifoil last?
- Manufacturer warranties run to 50 years on the foil layer itself. Because there is no binder to break down, no fibre to compress, and no moisture absorption, there is no practical reason it would degrade earlier.
- Will OMEGA remove my existing mineral wool when we fit multifoil?
- Sometimes — it depends what is up there. If the existing wool is dry, uncompressed, and at adequate depth, we typically leave it in place at floor level and fit the multifoil between or under the rafters. The combined effect is better than either material alone. If it is compressed, contaminated, or wet, we remove it and the loft starts clean.
Book a free home energy survey and we will lift the boards, photograph what is up there, and tell you on the day which answer suits your home.
Want to find out how much you could save?
Book a free 45-minute survey. We’ll check every active grant, measure every wall, and write you a plan. Yours to keep whether you book or not.
The plan is yours to keep. Take it to two other installers if you like.