The Practical Guide to UK Home Insulation: What I Use, Trust & Avoid

Insulation isn’t glamorous, but it’s one of the biggest upgrades you can make to a UK home — warmer winters, cooler summers, lower bills, and a house that actually feels comfortable instead of “just put a jumper on” cold. Whether you’re renovating, converting a loft, or sorting out a draughty outbuilding, good UK home insulation is the foundation that makes everything else work properly.

Why Insulation Matters

Most UK homes lose heat far faster than people realise, especially older properties. Good insulation tackles three big issues at once: it keeps heat inside, prevents condensation and damp, and brings energy bills down. It’s one of the simplest upgrades that makes a home feel instantly more comfortable and far cheaper to run.

Any brands mentioned in this guide — such as Knauf, Isover, Rockwool, Celotex, Kingspan, Actis and others — are simply examples I’ve used on various jobs over the years. They’re not endorsements, and there are plenty of other manufacturers offering similar products. Always check what’s available locally and what suits your project best.

Mineral Wool

Mineral wool is one of the most common insulation materials I use, and it comes in two main types: glass wool and stone wool. Glass wool (like Knauf Earthwool or Isover Spacesaver) is soft, flexible, and easy to fit between joists or studs. It’s ideal for loft floors, stud walls, and suspended floors.

Stone wool (such as Rockwool RWA45) is denser and heavier, and I use it when I need better soundproofing or fire resistance — external walls, floors, and outbuildings benefit from it.

It’s not the nicest material to handle — it can be itchy and irritating on the skin — so I always wear long sleeves, gloves, and a mask.

PIR Boards

PIR is a rigid, high‑performance foam board, and it’s one of my personal favourites to work with. Brands like Celotex, Kingspan, and Recticel are the ones I see most often.

I use PIR when I need strong thermal performance without eating up too much space — warm roof systems, loft conversions, external walls, and garden rooms are all places where it shines. It’s clean, predictable, and easy to cut accurately, which makes it ideal for tight build‑ups where every millimetre counts.

Fibreglass Insulation

Fibreglass is similar to glass mineral wool but slightly different in structure. It’s lightweight, affordable, and very common in loft floors (which are technically ceilings). Fibreglass rolls are easy to lay and great for topping up existing insulation.

It’s a straightforward, budget‑friendly option for homeowners who want a simple improvement without overthinking it.

Sheep’s Wool

Sheep’s wool is the natural, eco‑friendly alternative.

I haven’t used it personally, but it’s a solid choice for anyone who wants a sustainable material with a softer, more natural feel. It does cost more than mineral wool, but you’re paying for the environmental benefits and comfort.

Multifoil Insulation

Multifoil insulation is made from layers of reflective foil and wadding — SuperFOIL is a well‑known UK brand.

I’ve used multifoil in situations where space is tight or where radiant heat needs to be controlled, but it’s not a miracle product. It works best as part of a layered system, not as a standalone replacement for proper insulation like PIR or mineral wool. Used correctly, it can be a useful addition, but it shouldn’t be relied on by itself.

Spray Foam

Spray foam expands to fill awkward gaps and irregular spaces, creating an airtight seal.

I’ll be honest — I’m not a fan. When spray foam is applied between rafters, it blocks the ventilation gap, and over time that can cause the rafters to rot. It also affects roof breathability and can create mortgage issues. For me, it’s a firm no unless there’s a very specific reason to use it.

Hybrid Honeycomb Insulation (Actis Hybris)

Hybris is a modern honeycomb‑style insulation from Actis. It’s not mineral wool and it’s not PIR — it sits somewhere in between.

I’ve used Hybris on several projects recently, especially as PIR prices have climbed. It’s lightweight, clean to handle, and the honeycomb structure traps air effectively. It fits neatly between studs and rafters without slumping or shedding dust, which makes installation quick and tidy.

It works well in timber‑frame walls, pitched roofs, loft conversions, and garden rooms. It doesn’t quite match PIR for sheer thermal performance at the same thickness, but it’s a solid, dependable option — and it really comes into its own when you pair it with Actis’ HControl  and BoostR membranes , which help keep moisture in check and improve the overall build‑up.

 The Main Types of Insulation

Wall Insulation

Walls are a bit more nuanced. Cavity walls can be filled, but I’m personally not a fan of blown‑in insulation. It often creates cold bridging, leaving the outer skin exposed to cold, wet weather — which defeats the whole purpose of having a cavity in the first place. For stud walls, PIR boards work well on external walls, while mineral wool or fibreglass is usually the better choice internally.

Floor Insulation

Floors get overlooked far too often, but insulating them properly makes a huge difference to how warm a home feels.

On ground floors, I usually fit PIR boards between the joists because they give you strong performance without adding too much depth. For suspended floors, mineral wool works well because it helps cut down draughts and stops heat disappearing through the gaps.

For loft floors — which are technically ceilings — fibreglass is the simplest and most cost‑effective option for topping up what’s already there.

Outbuildings & Garden Rooms

This is where people tend to underestimate what’s needed. A garden office or studio needs a proper build‑up, not just “some insulation thrown in”.

PIR is great when you want high performance in a slim space, and mineral wool is a good option when you want to keep costs down or improve sound control. But the real key is the vapour control layer — without that, you’ll end up with condensation inside the structure no matter what insulation you choose.

Common Insulation Mistakes

I see the same problems crop up again and again: missing vapour barriers, no ventilation, the wrong material in the wrong place, or insulation that’s been compressed so much it barely works.

A vapour barrier is simply a thin sheet that stops warm, moist indoor air from drifting into the walls or roof. If that moisture hits something cold inside the structure, it can turn into condensation, which is where damp, mould and timber rot start. It sits on the inside, just behind the plasterboard, and needs to be sealed properly so moisture can’t sneak through gaps.

Ventilation on the cold side is still essential so any stray moisture can escape.

Even the best insulation performs badly if it’s installed poorly. A cheaper material installed correctly will always beat a premium material installed badly.

Loft Conversions

Loft conversions need a proper layered approach to work as they should. That usually means insulation between the rafters, another layer underneath, a vapour control layer, a ventilation gap, and insulated dwarf walls and floors.

Most DIY attempts fall down on ventilation and moisture control — and those two things are absolutely critical in a loft space.

Insulating Outbuildings, Sheds & Garden Rooms

If you want a garden room that’s genuinely usable all year round — not freezing in winter or roasting in summer — you need the full build‑up. That means proper insulation, a vapour control layer, a breathable membrane, good airflow, and insulation in both the floor and the roof.

Skip any of those layers and you’re asking for condensation, mould, or warped timber.

Seasonal Insulation Tips

In spring, it’s worth checking for damp patches, making sure roof ventilation is clear, and looking for any sagging insulation. Autumn is the time to top up loft insulation, seal draughts, and check outbuilding roofs before the cold sets in. During winter, keep an eye on condensation and cold spots around windows. In summer, roof insulation becomes your best friend for keeping overheating under control.

The Wrap-Up

Insulation isn’t just about staying warm. It protects your home, reduces your bills, and makes every space more usable throughout the year. Whether you’re converting a loft, building a garden room, or simply topping up what you’ve already got, doing it properly is what makes the real difference.