The short version
Mineral wool (glass or stone wool) works by trapping air in thick, fluffy layers. Current guidance for a typical loft is around 270mm of it, laid between and over the ceiling joists. SuperFoil is a multi-layer foil insulation that is far thinner, which is why it is popular where space matters, such as raised boarding, loft rooms and tight roof voids.
Neither is “best” for every home. The right choice depends on how you use the loft, how the roof is built and what condition it is in.
How each one works
- Mineral wool resists heat flow by holding still air within its fibres. It needs depth to perform, so a deep layer is the norm.
- SuperFoil combines layers of reflective foil with wadding or foam, reducing heat transfer by several routes at once, so it can be much thinner for comparable results. As with any product, performance claims depend on how it is installed, so ask for the specification for your roof.
Where SuperFoil makes sense
- You want to use the loft. A thin layer leaves headroom and avoids burying joists under 270mm of wool, which makes storage and boarding awkward.
- Space is tight. Low or shallow roof voids can be hard to insulate to full depth with wool.
- You are insulating at rafter level. It suits warm loft spaces and conversions where thickness is limited.
Where mineral wool still wins
- Plain, unused lofts. If nobody goes up there, deep wool laid on the loft floor is a proven, widely used approach.
- Budget-led jobs. For a straightforward, empty loft it can be a lower-cost option.
Whichever you choose, the biggest performance killer is poor installation: gaps, compressed layers and blocked eaves ventilation.
Condensation and ventilation
Warm, moist air from the house rises into the loft. Any loft insulation job should keep ventilation paths open at the eaves and avoid trapping damp against the roof timbers. Ask any installer how they deal with this, because a thick wool layer that blocks the eaves can cause as many problems as it solves.
If your loft already has spray foam under the roof, it is a different situation and can cause mortgage and survey problems. Our sister company covers that at igloosprayfoamremoval.co.uk.
Cost and installation compared
Mineral wool is usually cheaper per square metre of material and is laid in rolls by hand, so a simple empty loft can be quick to do. SuperFoil is a more specialist product fitted in a particular way, with overlaps sealed and gaps managed, so installer skill matters more. That is one reason to choose an accredited installer rather than the lowest quote.
Do not compare prices in isolation. Compare what each option will give you in warmth, usable space and long-term performance for your loft.
Which roofs suit which
- Standard cold loft, rarely used: deep mineral wool at ceiling level is the traditional answer.
- Cold loft you want to board: thin insulation plus a raised platform keeps floor height manageable.
- Low or awkward roof void: a thin product is often the only way to improve insulation without losing all your headroom.
- Rooms in the roof or warm lofts: thickness limits at rafter level favour slimmer products, with ventilation planned carefully.
Common mistakes with any loft insulation
- Blocking the eaves. Stuffing insulation into the eaves stops air moving and invites condensation.
- Leaving gaps. Missed corners, pipework and around the hatch are where heat escapes.
- Compressing it. Boards or stored items crushing the layer reduce its performance.
- Covering problems. Insulating over damp, leaks or damaged timber hides issues that will get worse.
- Forgetting the hatch. An uninsulated, leaky hatch undoes good work around it.
Questions to ask any installer
- What product and specification do you recommend for my loft, and why?
- How will you keep eaves ventilation open?
- How will you deal with pipes, cables and recessed lights?
- Will you inspect the roof timbers and felt before insulating?
- What guarantee and paperwork do I get?
How to choose
- Decide how you will use the loft: untouched, occasional storage or a proper space.
- Check how much headroom and depth you have.
- Get a survey so the loft’s condition and ventilation are checked.
- Compare quotes on specification, not just price.
We are SuperFoil accredited, so book a free survey and we will tell you plainly whether SuperFoil suits your loft or not. Read more about our SuperFoil loft insulation.