If you’re insulating an attic, a wall, or a garage ceiling in the GTA, you’ve probably run into two very different answers from two different contractors: one pushes spray foam, the other pushes blown-in. Both are legitimate products. Neither is automatically “better” — they solve different problems, and the contractor who tells you that upfront is more trustworthy than the one who has a single answer for every home.
This guide breaks down what each material actually is, where each one wins, and where each one falls short, so you can walk into a quote already knowing what questions to ask.
The Quick Answer
Blown-in insulation is loose-fill cellulose or fiberglass, machine-blown into an attic or cavity. It’s the lower-cost, faster-install option, and it’s the standard choice for a straightforward attic that needs more R-value and doesn’t have a draft or moisture problem.
Spray foam insulation is a two-part liquid that expands and cures into a solid layer, insulating and air-sealing in the same step. It costs more and requires a licensed applicator, but it earns that cost back in homes with complex rooflines, persistent drafts, or moisture-sensitive areas like garage ceilings and rim joists.
Neither one is the “upgrade” version of the other — they’re built for different jobs.
What Is Blown-In Insulation?
Blown-in insulation is loose-fill material — either cellulose or fiberglass — installed with a blowing machine that fills attic spaces and works around joists, wiring, and awkward framing. It’s the most common attic upgrade in the GTA because most existing attics simply need more R-value, not air sealing, and blown-in delivers that at a lower cost per square foot than foam.
Cellulose, made primarily from recycled paper, has a higher R-value per inch (roughly R-3.4 to R-3.8) than fiberglass (roughly R-2.7 to R-3.0). Both materials are effective, both are accepted under most rebate programs, and both can typically be blown directly over existing insulation without removing it first, as long as the existing material isn’t contaminated.
What Is Spray Foam Insulation?
Spray foam insulation works on a completely different mechanism. Two chemical components are combined at the spray gun tip and expand on contact, filling cavities and curing into a solid, adhered layer. Because it expands into gaps and cracks as it cures, it insulates and air-seals in a single application — something blown-in and batt insulation don’t do on their own.
There are two common formulations:
- Open-cell (1/2 lb, low-density): Lighter, more flexible, and typically the lower-cost foam option. Common in interior walls and some attic applications where air sealing is the priority.
- Closed-cell (2 lb, high-density): Denser, higher R-value per inch, and rigid enough to act as its own vapour barrier at sufficient thickness — the standard choice for basements, crawlspaces, rim joists, and garage ceilings where moisture control matters as much as heat retention.
Unlike blown-in insulation, spray foam is not a realistic DIY project, and it isn’t forgiving of a rushed installation — a poor application generally has to be cut out and redone rather than topped up. That makes the installer’s experience a bigger factor in the outcome than it is with blown-in material.
Spray Foam vs. Blown-In: Side-by-Side
| Factor | Blown-In (Cellulose/Fiberglass) | Spray Foam (Open/Closed-Cell) |
|---|---|---|
| Air sealing | No — insulates only | Yes — insulates and air-seals in one step |
| Cost per square foot | Lower | Higher |
| Install speed | Fast — typically same-day for most attics | Slower, more labour-intensive |
| Moisture/vapour barrier | No | Closed-cell only, at sufficient thickness |
| Best for irregular framing | Fair — can leave gaps around complex framing | Strong — expands to fill gaps |
| Settling over time | Can settle and thin slightly | Does not settle once cured |
| DIY feasibility | Not recommended, but simpler | Not a DIY project |
| Rebate eligibility | Commonly accepted | Often eligible, program-dependent |
Pros and Cons of Blown-In Insulation
Pros
- Lower cost per square foot than spray foam
- Fast installation — most standard attics are done in a day
- Effective at filling gaps around joists, wiring, and uneven framing
- Can usually be added directly over existing insulation without removal
- Widely accepted under Ontario rebate programs
Cons
- Does not air-seal — drafts and air leakage go untouched
- Can settle and lose some loft (and R-value) over time
- Offers no moisture or vapour barrier on its own
- Less effective in attics with significant draft or airflow problems
Pros and Cons of Spray Foam Insulation
Pros
- Insulates and air-seals in a single application
- Closed-cell foam acts as its own vapour barrier at sufficient thickness
- Expands into irregular framing, additions, and complex rooflines that blown-in can leave gapped
- Does not settle or lose R-value once cured
- Strong fit for moisture-prone areas like garage ceilings and rim joists
Cons
- Higher cost per square foot than blown-in insulation
- Not a DIY-friendly product — application technique affects the outcome directly
- A poor installation usually has to be cut out and redone, not patched
- Overkill (and an unnecessary expense) for a simple, regularly shaped attic with no draft or moisture issues
So Which One Should You Choose?
This comes down to what problem you’re actually solving, not which material sounds more advanced.
Blown-in is usually the right call when: your attic is a regular shape, insulation levels are simply low or settled, and you’re not dealing with drafts, cold rooms, or moisture. This describes a large share of attic upgrades in the GTA’s older housing stock — the fix is more material, not a different material.
Spray foam earns its higher cost when: you have a complex roofline or addition where framing doesn’t line up cleanly, persistent drafts that weatherstripping hasn’t solved, a cold room above an attached garage, or a moisture-sensitive cavity like a rim joist. In these cases, the air-sealing function is doing real work that blown-in physically cannot do.
A contractor who recommends spray foam for every job — or blown-in for every job — is optimizing for their own preferred product, not your attic.
A Note on Cost
Exact pricing depends on square footage, attic accessibility, existing insulation condition, and which specific product is used — a number quoted here without a real estimate would be a guess, not a fact. The directional point — that spray foam costs more than blown-in per square foot — is a well-established industry fact and is safe to state without a specific number attached.
A Note on Rebates
Ontario has active rebate programs that can offset part of an insulation upgrade, including options referenced on our home renovation savings and Greener Homes Loan pages. Eligibility depends on the specific program, the product installed, and how the job is documented — and these programs change terms over time.
FAQ
Can I combine blown-in and spray foam in the same job? Yes — it’s common to use spray foam at specific problem areas (a rim joist, a garage ceiling, an addition) and blown-in across the main attic field. This isn’t an either/or decision for every square foot of a home.
Do I need to remove my existing insulation before adding either type? Not usually. Existing insulation can typically be insulated over unless it’s contaminated by moisture, pests, or mold — in that case, attic insulation removal needs to happen first.
Is spray foam always better because it’s more expensive? No. Cost reflects the extra labour and air-sealing function, not a universal quality upgrade. A simple, regularly shaped attic with no draft or moisture issues is often better served by blown-in insulation at a lower cost.
Which one is right for my home? That depends on your attic’s shape, your existing insulation condition, and whether drafts or moisture are part of the problem — not something to guess from a blog post. A free in-home inspection is the only way to get a real answer.