Insulation types explained: batts, blanket and board
What R-value really means and where each type of insulation goes in a new home, so you can read your spec and check it adds up.
Insulation is the quiet workhorse behind a comfortable, efficient home, and it is doing most of the job of hitting your 7-star rating. The spec sheet throws around terms like batts, blanket and R-values, which can feel like a foreign language. Here is what they mean and where each type belongs, for homes across SA and Victoria.
Bulk vs reflective insulation
Bulk insulation, like batts, traps air in its fibres to slow heat moving by conduction, and it carries an R-value. Reflective insulation, like foil sarking, works by reflecting radiant heat across an air gap rather than absorbing it. They tackle heat in different ways, which is why a well-built roof often uses both: a reflective layer under the roof to bounce radiant heat and bulk batts in the ceiling to resist the rest. One is not a substitute for the other.
Glasswool vs polyester batts
At the same R-value, glasswool and polyester batts insulate much the same, so the choice is about handling and preference. Glasswool is widely available and good value but can irritate skin during the install. Polyester is softer, itch-free and often made with recycled content, which some owners prefer for bedrooms or for a healthier install, at a slightly higher cost. Match the R-value your assessment calls for and pick the material you are comfortable with.
Wall vs ceiling insulation
Both matter, but the ceiling usually gives you the most comfort per dollar because a lot of heat is gained and lost through the roof. Walls still need their rated batts, and they are easy to insulate well in a framed wall while it is open. The practical rule is simple: do not skimp on either, because your energy rating assumes both are there, and a well-insulated ceiling over poorly insulated walls leaves comfort on the table.
External vs internal wall insulation
In most Australian new homes, wall insulation sits inside the framed cavity, which is simple and effective. External wall insulation, where an insulating layer wraps the outside of the structure before cladding or render, is less common here but can reduce thermal bridging and add continuous cover, which suits high-performance and some masonry builds. For a standard framed home the in-cavity approach is the norm; external systems are a specialist choice.
Ceiling insulation R5 vs R6
R6.0 ceiling batts resist a bit more heat flow than R5.0 and are now common in new SA and Victorian homes, often for only a small step up in cost. The extra is usually worth taking in the ceiling, where it does the most good. That said, the gain from a higher number is quickly lost if the batts are installed with gaps or squashed around downlights, so a neat install matters as much as the R-value you choose.
What R-value means
R-value measures how well a material resists heat flow. The higher the number, the better it insulates. Your climate zone sets minimum R-values for the roof, walls and sometimes the floor, and your NatHERS assessment works out the mix that gets the home to 7 stars. More is not always better in every spot, the goal is the right R-value in the right place.
Where each type goes
Bulk batts do the heavy lifting in framed walls and ceilings. A roof blanket sits under the roof sheets to knock back radiant heat and, on a metal roof, to soften rain noise. Rigid board turns up in specific spots like slab edges or where space is tight and you need high performance in a thin layer.
Why installation is everything
The best insulation in the world does nothing if it is installed badly. Gaps, gaps around downlights, and batts that are squashed into place all cut the real-world performance well below the rating on the label. It is worth asking who installs it and whether the ceiling is checked after the trades have been through, because this is where a lot of homes quietly lose comfort.
Bulk batts (walls and ceilings)
- The workhorse for walls and ceilings
- Comes in a range of R-values to suit the zone
- Easy to install in framed walls
- Good value for the performance
- Only works if installed with no gaps or compression
- Does not stop air leaks on its own
Roof blanket (under the roof)
- Sits under the roof sheets to cut radiant heat
- Helps with rain noise on metal roofs
- Works alongside ceiling batts
- Not a substitute for ceiling insulation
- Needs the right facing for the job
Rigid board (slabs, special spots)
- High performance in a thin profile
- Used at slab edges and tricky details
- Rigid and moisture resistant
- Used selectively, not everywhere
- A more specialised product
Insulation is not the place to cut corners, because it is doing most of the work on comfort and your energy rating for the life of the home. Get the R-values your NatHERS assessment calls for, make sure the ceiling and walls are installed with no gaps or compression, and treat a quick post-install check as time well spent.
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What is the difference between bulk and reflective insulation?
Bulk insulation like batts traps air to slow conducted heat and has an R-value. Reflective insulation like foil sarking reflects radiant heat across an air gap. They work differently, so a good roof often uses both: a reflective layer under the roof and bulk batts in the ceiling.
Is glasswool or polyester insulation better?
At the same R-value they perform much the same. Glasswool is cheaper and widely available but can irritate skin during the install. Polyester is softer, itch-free and often recycled, at a slightly higher cost. Choose the R-value your assessment needs and the material you are comfortable with.
Is R6 ceiling insulation worth it over R5?
Usually yes. R6.0 resists a little more heat flow than R5.0 and is now common in new homes for a small step up in cost, and the ceiling is where it does the most good. Just make sure it is installed with no gaps or compression, or the extra rating is wasted.
What does R-value mean in insulation?
R-value measures how well a material resists heat flow. A higher number insulates better. Your climate zone sets minimum R-values and your NatHERS assessment works out the right mix for the roof, walls and floor to reach 7 stars.
What is the difference between batts and a roof blanket?
Bulk batts go in framed walls and ceilings to resist heat flow. A roof blanket sits directly under the roof sheets to cut radiant heat and, on metal roofs, soften rain noise. They do different jobs and often work together.
Is more insulation always better?
Not necessarily. The aim is the right R-value in the right place, as worked out by your NatHERS assessment. Beyond a point, extra insulation in one spot adds little while good installation and sealing air gaps matter more.
Why does insulation installation matter so much?
Gaps, compression and missing insulation around downlights can drop real performance well below the label rating. A careful install, and a check of the ceiling after the trades finish, is one of the best ways to protect your comfort and energy rating.
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Sources last verified June 2026