Blown-in vs batt insulation
What each type is, where each wins, and how to work out how much you need — without anyone telling you the R-value your code already sets.
The short version
Blown-in (loose-fill) — cellulose or fibreglass poured or blown to a depth. Best for open attic floors: it fills around obstructions with no seams and covers large areas fast.
Batts and rolls — pre-cut sections sized for stud and joist bays. Best for walls and tidy, regular bays where you want a known, uniform thickness and no equipment.
Both reach the same R-value if installed well. The real difference is how completely they fill the space — and gaps, not the product, are what quietly drop performance.
Where each one wins
| Blown-in | Batt / roll | |
|---|---|---|
| Open attic floor | Best — fills gaps, fast | Works, slower, more gaps |
| Walls (open framing) | Needs netting | Best — cut to the bay |
| Around wires/pipes/obstructions | Best — flows around | Must cut and fit carefully |
| Equipment needed | A blower | None |
| Small, regular space | Overkill | Best |
The thing that actually matters: gaps
A batt crammed around a wire, compressed by a pipe, or left short at the end of a bay loses R-value exactly where the gap is. Blown-in avoids most of this because it has no seams. If you use batts, cut them to fit and split them around obstructions rather than stuffing them. Whichever you pick, air-seal penetrations first — insulation slows heat, it does not stop air leaks.
How much to buy
Quantity comes from the area and the coverage printed on your product at your target R-value — not from the type. The insulation calculator does it for either one, and insulation by attic size has worked bag counts for common attics. Your required R-value is set by your local code and climate zone — see how to find the R-value you need.
Questions
Is blown-in or batt insulation better for an attic?
For an open attic floor, blown-in (loose-fill) usually wins: it fills gaps and around obstructions with no seams, and it is fast to install over a large area. Batts make sense in walls and in tight, regular joist bays where you want a known thickness. Both reach the same R-value — the difference is how well they fill the space and how much air leaks through gaps.
Which gives better coverage with fewer gaps?
Blown-in. Because it is poured or blown to a depth, it flows around wiring, pipes and odd framing with no cut seams. Batts have to be cut to fit, and every gap, compression or gap behind a wire lowers the real-world R-value. In an attic with lots of obstructions, blown-in is more forgiving.
Is blown-in cheaper than batts?
Material cost per R-value is similar; the difference is labour. Blown-in needs a blower (often free to borrow with a bulk purchase) and is quick over a big attic. Batts need no equipment but take longer to cut and fit well. For a small, regular space batts can be cheaper; for a large attic, blown-in is usually faster and therefore cheaper to install.
How many bags or rolls do I need?
That comes from your area and the coverage on the product, not from the type. Use the insulation calculator: enter the area and the coverage printed on your bag or roll at your target R-value, and it gives the number to buy.