Imagine you are finishing a granny flat or a backyard shed. If you just put up plasterboard, that room will be unusable for half the year. By sliding Foilboard into the walls or under the floorboards, you aren’t just adding a “layer”; you are creating a thermal shield.
But what is Foilboard?
Foilboard Insulation Green Rigid EPS Panels
Foilboard is a rigid insulation sheet made of a foam core (EPS) sandwiched between two layers of heavy-duty aluminium foil.
Think of it like a thermos for a house. It’s a solid panel—not a soft blanket—that comes in different thicknesses (usually 10mm to 25mm for residential). It’s designed to replace or work alongside traditional “itchy” batts. Because it’s rigid, it won’t sag over time, and because it’s foil-faced, it reflects heat like a mirror.
How does Foilboard work?
Foilboard works by reflecting 97% of radiant heat away from the building while the foam core stops heat from “soaking” through the walls.
In the middle of a Sydney or Brisbane summer, the sun bakes your brickwork. That heat wants to move inside. The silver face of the Foilboard reflects that heat back out. In winter, it does the opposite. It keeps the warmth you’ve paid for inside the room. For it to work perfectly, you need to leave a small air gap (usually 20mm) between the foil and the next surface. That gap is where the magic happens.
Where should you use it?
Foilboard is most commonly used in wall cavities, under suspended timber floors, and in shed or garage fit-outs.
Underfloor: If you have a house on stumps in Melbourne or Adelaide, Foilboard is a lifesaver. It stops the wind from blowing up through the floorboards.
Walls: It’s great for brick veneer or double brick walls because it’s thin enough to fit in the cavity while providing a massive boost to the R-value.
Sheds: If you’re turning a tin shed into a workspace, lining it with Foilboard is the quickest way to stop it from becoming an oven.
Why choose Foilboard over traditional batts?
Foilboard is better than batts because it’s moisture-proof, it doesn’t sag, and it is much thinner for the same level of performance.
No Itch: You can handle Foilboard in a t-shirt.
Waterproof: It doesn’t care if it gets rained on during the build.
Permanent: Unlike batts, which can slump to the bottom of a wall cavity after five years, Foilboard stays exactly where you nail or clip it.
How do you install it?
You don’t need fancy tools. Here is the “builder’s’ speed” method:
Cut to Size: Use a standard utility knife and a straight edge. It cuts cleanly without leaving a mess of fibres all over the site.
Set the Gap: Use Foilboard spacers for walls or saddle clips for underfloor joists. These are essential because they hold the board away from the surface, creating the air gap needed for the foil to reflect heat.
Fasten: Fix the boards in place using the recommended fasteners for your specific frame (timber or steel).
Seal the Joins: This is the most critical step for performance. You must use Foilboard Green Joining Tape on all seams and joints. This specific tape is designed to stick to the foil surface permanently, creating an airtight seal that prevents heat leakage and moisture from getting behind the boards. If you don’t tape it, you’re losing energy.
Foilboard vs. Other Insulation
Foilboard is the best choice when you have limited space or need a material that won’t be damaged by moisture, while batts are fine for big, open roof spaces. If you’re building a modern home with slim walls, you probably won’t fit enough glasswool in there to meet the energy ratings. Foilboard solves that. It’s also the “pro” choice for underfloor jobs because it’s much more durable against the elements than other flexible foil products.
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