The Cheapest Ways to Insulate Internal Walls (DIY Guide for 2025)
Looking to make your home more comfortable without spending a fortune? Insulating your internal walls is one of the easiest and most cost-effective ways to improve year-round comfort. Whether it’s keeping the heat in during winter or blocking out summer heat, proper insulation helps regulate indoor temperature, reduce energy bills, and add acoustic comfort — and yes, you can do it yourself.
In this guide, we’ll cover affordable insulation options, real product examples, and what kind of R-values you can expect, so you can make smarter upgrades without breaking the bank.
Let’s break down the best low-cost insulation methods, how they compare, and which products give the biggest energy savings for the least money.
✅ Why Insulate Internal Walls?
🏡 Keep heat inside during colder months
Proper insulation traps heat, preventing it from escaping through the walls. This is especially crucial during the winter months when heating costs can skyrocket. Insulating your internal walls ensures a warmer home and keeps energy use to a minimum.
🔇 Improve soundproofing between rooms
Insulating walls can help reduce noise from one room to another. This is particularly beneficial in shared living spaces, offices, or rooms where you want to block out external noise. Materials like mineral wool and foam boards can significantly dampen sound and reduce disturbances.
💷 Reduce heating bills (especially in older homes)
Older homes, especially those with brick or poorly insulated walls, can be major culprits for heat loss. By improving internal wall insulation, you can keep the warmth in and reduce the need for constant heating, ultimately lowering your energy bills.
🌱 Choose eco materials for a greener upgrade
Many insulation materials today are made from environmentally friendly sources, like recycled denim or natural fibers, allowing you to make a sustainable choice while improving your home’s energy efficiency.
Even one well-insulated room can make a noticeable difference, and it doesn’t have to involve heavy tools or full renovations.
🔍 How Your Current Wall Performs
Before you start insulating, it’s important to understand how your current walls perform in terms of heat retention. Most UK homes have solid brick or cavity walls with plasterboard. Here’s how they compare in insulation performance:
| Wall Type | Approx. R-Value |
|---|---|
| Bare brick + plasterboard | R ≈ 0.5–0.8 |
| Brick + 25mm air cavity (uninsulated) | R ≈ 0.9 |
| Brick + insulated foam board (50mm+) | R ≈ 2.0–3.0 |
To noticeably improve warmth and efficiency, aim for an R-value above 1.8. The higher the R-value, the better the insulation’s ability to resist heat flow.
💸 DIY Wall Insulation: Products Compared
Here’s a breakdown of some of the most affordable and effective insulation products, their approximate R-values, thickness, and costs:
| Product Type & Brand | R-Value (Approx.) | Thickness | Cost per m² | Best Use |
|---|---|---|---|---|
| Wallrock Thermal Liner | R ≈ 0.3–0.5 | 4–10mm | £4 – £8 | Rented flats, retrofits |
| Jablite EPS70 Foam Board | R ≈ 0.9 | 30mm | £6 – £12 | Behind plasterboard or cladding |
| Celotex GA4000 PIR Board | R ≈ 2.25 | 50mm | £10 – £15 | High-performance insulation |
| EcoQuilt Expert (Multifoil) | R ≈ 1.5–2.0 (with air) | 30–40mm | £8 – £12 | Under battens or drylining |
| Rockwool Flexi Batts | R ≈ 2.25 | 100mm | £5 – £10 | Stud walls + soundproofing |
| Foil Bubble Wrap (EcoTec) | R ≈ 0.8–1.2 (radiant) | 4–7mm | £2 – £4 | Behind radiators or voids |
| Thermafleece (Recycled Denim) | R ≈ 2.0 | 100mm | £8 – £15 | Natural + breathable insulation |
These are the most common products you can use to insulate internal walls on a budget, with varying degrees of performance and cost.
🔨 Top 7 DIY Methods (With Real Products)
Here are some of the most cost-effective ways to insulate your internal walls, along with real product examples you can purchase for your DIY project:
Wallrock Thermal Liner
A thick wallpaper roll that insulates without making a mess. It’s a simple, quick fix for renters or people who don’t want to commit to a full renovation. Best For: Flats, rentals, easy retrofits
Pros: Easy install, paintable
Cons: Lower R-value, not for moist walls
Tip: Combine with thermal paint to boost results
Buy Wallrock Thermal Liner
Jablite EPS70 Foam Boards
Expanded polystyrene boards are cheap and surprisingly effective. These are often used for wall upgrades behind plasterboard or cladding. Best For: Under plasterboard or behind panels
Pros: Lightweight, affordable
Cons: Needs sealing around edges
Tip: Pair with foil layer for heat reflection
Buy Jablite Foam Boards
Celotex GA4000 PIR Boards
Rigid insulation with excellent thermal performance per mm. These boards have a higher R-value and are ideal for internal wall upgrades. Best For: Full internal wall upgrades
Pros: High R-value, long-lasting
Cons: Slightly pricier, needs accurate cutting
Tip: Screw battens over boards then fix plasterboard
Buy Celotex PIR Boards
EcoQuilt Expert Multifoil
Reflective insulation with multiple foil layers and padding. This is a lightweight material that reflects heat while providing an air gap for better efficiency. Best For: Radiant heat control, thin walls
Pros: Reflects heat, lightweight
Cons: Needs air gap + stapling to battens
Tip: Works best between timber studs
Buy EcoQuilt Multifoil
Rockwool Flexi Batts
Mineral wool that’s great for both thermal and sound insulation. These batts are non-combustible and provide a great balance of cost, performance, and ease of installation. Best For: Hollow walls and timber studs
Pros: Fire-safe, sound dampening
Cons: Itchy during install (wear gloves/mask)
Buy Rockwool Acoustic Insulation Slab
Foil Bubble Wrap (EcoTec)
An ultra-thin barrier you can staple to the back of drywalls or radiators to reflect heat. It’s very affordable and works well for smaller areas. Best For: Radiator backs, sheds, quick wins
Pros: Very cheap, easy to cut
Cons: Low performance without air gap
Buy Foil Bubble Wrap
Thermafleece Recycled Denim
Sustainable insulation made from recycled jeans. It’s breathable and non-toxic, making it ideal for eco-friendly homes. Best For: Eco homes, breathable walls
Pros: Non-toxic, retains heat well
Cons: Needs dry conditions, not for wet walls
Buy Thermafleece Cosywool
🛠 Tools You’ll Need
When it comes to installing insulation, here are the essential tools:
- Tape measure: To measure your walls before purchasing insulation materials
- Sharp blade or insulation knife: For cutting materials like foam boards and batt insulation
- Spray adhesive or fixings: For sticking insulation to your walls
- Staple gun: For securing foil or multifoil insulation
- Gloves and dust mask: For protection when handling mineral wool or other fibrous materials
🧠 Bonus Tips
- Seal all gaps and cracks before installing
Ensure the integrity of your wall by sealing any gaps or cracks around windows, doors, or joints. Gaps can let air leak in or out, reducing the effectiveness of your insulation. - Use a foil + foam board combo
A combination of reflective foil and foam boards can significantly improve insulation efficiency. The foil reflects heat, while the foam provides thermal resistance. - Add rugs and heavy curtains to improve heat retention
After insulating your walls, you can further reduce heat loss by adding thick rugs and curtains to your rooms. These act as additional layers of insulation, keeping your space warmer. - Consider thermal curtain linings or magnetic secondary glazing
Secondary glazing or thermal curtain linings can help keep rooms cooler in the summer and warmer in the winter by reducing heat transfer through windows.
📝 Conclusion
You don’t need planning permission or a contractor to improve your home’s warmth. Even basic internal insulation with the right product can save money fast — and boost comfort in every room.
✅ Start with just one wall and see the difference.
👉 Want to go further? Read our Eco Heating Systems That Actually Save You Money next.
❓ Frequently Asked Questions
Q: What is the cheapest insulation for internal walls?
A: Foil bubble wrap (like EcoTec) and thermal liner wallpaper (like Wallrock) are among the cheapest options, costing as little as £2–£4 per m². They’re great for renters or quick fixes but have lower R-values than foam or mineral boards.
Q: What’s the best insulation for soundproofing internal walls?
A: Mineral wool (like Rockwool Flexi) is ideal. It not only insulates against heat loss but also significantly reduces sound transfer between rooms.
Q: Can I install insulation without removing plasterboard?
A: Yes! Many products — like Wallrock thermal liner or multifoil insulation — can be applied directly on top of existing walls using adhesive or battens.
Q: Will I save money by insulating just one wall?
A: You won’t cut your heating bill in half, but you will notice improved warmth and comfort, especially in colder rooms. It’s a smart place to start before committing to full-room upgrades.
Q: Is thicker insulation always better?
A: Not always. High-performance materials like PIR boards or multifoil can outperform thicker but cheaper materials. Also, if space is tight, you’ll want to balance thickness with practicality.
Q: Can I insulate a wall with damp issues?
A: No — always fix moisture problems first. Insulating a damp wall can trap moisture and make the problem worse, leading to mould and structural damage.
