Ecologic Guides · R-Values
Spray foam R-values: LTTR, test methods, and the numbers that count
Direct answer
Closed-cell spray foam insulates at roughly R-5 to R-6 per inch, and the honest way to state that is by thickness. The 2lb foam we install is rated R-5.3 at 1 inch, R-11.1 at 2, R-17.5 at 3 and R-24.1 at 4, long-term (LTTR) values tested under CAN/ULC-S770-15 and published on its CCMC listing. Foam R-values decline from their fresh-sprayed peak as the blowing agent slowly exchanges with air, so Canadian standards require a five-year design value rather than a day-one number. Per-inch performance also rises with thickness, which is why a single "R per inch" figure can mislead. Open-cell foam runs R-3.5 per inch. When you compare quotes, ask for the thickness-specific LTTR and the test method behind it.
Sources: CCMC 14133-L · CAN/ULC-S770-15 · manufacturer TDS 2024
01 First principles
What do R-value and RSI actually measure?
R-value measures how well a material resists heat flowing through it. Higher is better. If one wall is R-10 and another is R-20, the second loses heat at half the rate through its insulated area, all else being equal. It is a resistance number, the thermal equivalent of how hard it is to push water through a pipe.
Canada officially uses the metric version, RSI. The conversion is fixed: multiply RSI by 5.678 to get the imperial R-value. So RSI 1.92 is R-10.9, and the code's foundation-wall target of RSI 2.98 is R-16.9. Building codes, CCMC listings and Efficiency Manitoba paperwork all speak RSI; contractors and homeowners mostly speak R. Both appear on our quotes.
Two things R-value does not capture: air leakage and moisture. A batt rated R-19 does nothing about the air washing past it, and in most older Manitoba houses air leakage moves more heat than conduction does. That context matters later in this guide, because comparing foams to fibres on R-value alone misses half the physics. For the vocabulary along the way, our glossary defines every term on this page.
02 Aging
Why do foam R-values change over time?
Closed-cell foam owes its high R-value partly to the gas sealed inside its cells. The blowing agent that expands the foam stays trapped there, and it conducts heat more poorly than air does. That is the head start foam has over every fibre insulation.
The head start shrinks a little with time. Over months and years, blowing agent slowly diffuses out of the cells and air diffuses in. Fresh foam might test near R-7 per inch; the same foam years later settles lower. This is normal physics, not a defect, and it happens to every closed-cell foam and every foam board on the market.
The Canadian answer to this is LTTR: long-term thermal resistance. CAN/ULC-S770 ages thin slices of foam under controlled conditions to predict the R-value at five years in service, and that five-year figure becomes the design value. Codes, CCMC listings and rebate programs use LTTR precisely so nobody designs a wall around a day-one number that will not hold.
The three numbers a foam can carry
Initial R-value. Measured on fresh foam. Highest of the three. Legitimate for lab comparison, misleading on a quote.
LTTR (CAN/ULC-S770). The five-year design value from accelerated aging. This is the number codes and Efficiency Manitoba accept, and the only one we publish.
"Up to" marketing values. Whatever the brochure writer could defend on the best day. Not tied to a thickness, a method or a listing. Ignore these.
Aging is already priced into LTTR. A foam rated R-11.1 LTTR at 2 inches is expected to deliver about that for the life of the wall.
03 Thickness
Why "R per inch" is a slippery unit
The per-inch value of the same foam rises with thickness. Here is the full ladder for the closed-cell foam we install, with methods cited.
Blowing agent escapes through the surfaces of the foam. In a thin lift, every cell sits close to a surface, so the gas exchange runs faster and the aged R-value per inch lands lower. In a thick lift, the interior cells are buried behind inches of foam that slow the diffusion down, so more of the original gas stays put. The result shows up plainly in the test data: per-inch LTTR climbs as the foam gets thicker.
| Thickness | LTTR | Per inch | Method / source |
|---|---|---|---|
| 1 inch (25 mm) | R-5.3 | R-5.3 | CAN/ULC-S770-15 · TDS 2024 |
| 2 inches (50 mm) | R-11.1 (RSI 1.92) | R-5.6 | CAN/ULC-S770-15 · TDS 2024 + CCMC 14133-L design value |
| 3 inches (75 mm) | R-17.5 | R-5.8 | CAN/ULC-S770-15 · TDS 2024 |
| 4 inches (100 mm) | R-24.1 | R-6.0 | CAN/ULC-S770-15 · TDS 2024 |
| Open-cell (Grizzly 005), any inch | R-3.5/inch (RSI 0.61) | R-3.5 | ASTM C518 · TDS 2021 (open-cell is not LTTR-rated) |
Read the ladder and the problem with "R-6 per inch" becomes obvious. At 4 inches our foam does average R-6.0 per inch. At 1 inch it is R-5.3. A contractor quoting a 1-inch flash coat at "R-6 per inch" is borrowing the 4-inch number for a thickness where it does not apply. Thickness-specific values are the honest currency, which is why our quotes state the LTTR for the actual thickness being sprayed, never a per-inch shortcut multiplied out.
04 Test methods
Ask which test method a number comes from
The same foam, tested under two editions of the same standard, produces two different R-values. Our own product is the cleanest example we can offer.
CAN/ULC-S770 has been revised over the years, and the revisions changed the aging procedure. Under the 2003 edition (S770-03), the foam we install rated RSI 2.10 at 50 mm: R-12 at 2 inches, almost exactly R-6 per inch. That figure is where a generation of "R-6 per inch" marketing came from, ours included at one time.
Under the 2015 edition (S770-15), the current method, the same product rates R-11.1 at the same 2 inches. Nothing about the foam changed. The test got more conservative, and the number followed. We publish the S770-15 values because they are the current standard and the ones CCMC carries as design values, even though the older figure reads better on a brochure.
This is the single most useful question you can put to any insulation bidder: which edition of S770 is that R-value from? A contractor still quoting 2003-method numbers in 2026 is quoting a superseded test, and a contractor who cannot answer the question is reading a brochure to you. More questions like this one are in our guide to hiring a spray foam contractor.
One foam, two editions of the test
| Method | LTTR at 2 in (50 mm) | Status |
|---|---|---|
| CAN/ULC-S770-03 | RSI 2.10 (R-12) | Superseded |
| CAN/ULC-S770-15 | RSI 1.92 (R-11.1) | Current · what we publish |
The 0.9 R difference is the gap between "R-6/inch" marketing and the current design value. Same drum of foam either way.
05 The credible range
"Up to R-7 per inch" and other numbers to walk away from
You will see closed-cell foam advertised at "up to R-7 per inch." That is typically an initial value on fresh foam, or a best-case lab figure with no thickness attached. Building Science Corporation, the most-cited building physics consultancy in North America, puts credible aged values for 2lb closed-cell foam at R-5.5 to R-6.5 per inch. Our ladder sits inside that range. Numbers above it deserve a request for the test report.
Efficiency Manitoba settled this argument for practical purposes: the Home Insulation Rebate accepts only CCMC-published LTTR values and rejects declared or marketing R-values outright. If a quoted R-value cannot survive a rebate application, treat that as information.
One more comparison that needs context: open-cell versus closed-cell. Open-cell foam delivers R-3.5 per inch (ASTM C518), and on R-value alone it looks like half the product. But the two foams do different jobs. Closed-cell is a code-recognized vapour barrier at 2 inches (permeance 39 ng/(Pa·s·m²), under the 60 limit) and an air barrier at 1 inch; open-cell is vapour-open at 1,580 ng and needs poly in our climate, while bringing sound control and a lower price where vapour control comes from elsewhere. Comparing the two on R per inch without the vapour and air story is comparing a truck to a car by cupholders. The full closed-cell case is on our closed-cell page, and the blowing-agent chemistry behind aged R-values is covered in the HFO vs HFC guide.
06 Effective R
Effective R-value: what the wall does, not what the label says
The R-value on a batt label describes the insulation alone. A real wall also contains studs, plates, headers and rim material, and wood insulates at only about R-1.25 per inch. Every stud is a thermal bridge that short-circuits the insulation beside it. In a typical wood-frame wall, framing occupies roughly a quarter of the surface area.
NBC 9.36, the energy section Manitoba builds to, therefore sets its targets in effective R-value: the performance of the whole assembly with the bridging counted. A 2x6 wall full of R-19 batts does not perform at R-19; once the framing is averaged in, the wall lands meaningfully lower. Building Science Corporation's worked example for a spray-foamed frame wall shows an installed R-30 dropping to roughly R-20 for the whole wall once framing is counted.
This is where high per-inch materials earn their keep: when the cavity is shallow (a 2x6 wall, a rim joist, a basement furred at 2 inches), getting more R into the same depth lifts the effective number in a way adding a fourth label to the brochure never will. Our quotes show the effective math for your assembly against the code target.
07 Questions
R-values, answered
What R-value is spray foam per inch?
For the closed-cell foam we install, the honest answer is a ladder, not a single number: R-5.3 at 1 inch, R-11.1 at 2 inches, R-17.5 at 3 and R-24.1 at 4, all long-term (LTTR) values under CAN/ULC-S770-15. That works out to roughly R-5.3 to R-6.0 per inch depending on thickness. Open-cell foam is R-3.5 per inch (ASTM C518). Any per-inch figure quoted without a thickness and a test method is a marketing number.
Source: manufacturer TDS 2024 · CCMC 14133-L
What is LTTR?
LTTR stands for long-term thermal resistance. It is the R-value a foam insulation is predicted to have after five years in service, measured under CAN/ULC-S770 using accelerated aging of thin slices. Canadian codes and rebate programs use LTTR because foam R-values decline from their fresh-sprayed peak as the blowing agent slowly exchanges with air. LTTR is the design value, so the aging is already priced in.
Source: CAN/ULC-S770-15
Why do quotes show different R-values for the same thickness?
Usually one of three reasons: different products, different test methods, or different honesty. The same foam can carry an initial R-value, an S770-03 LTTR and an S770-15 LTTR, and the three numbers differ. Our own foam rated R-12 at 2 inches under the 2003 method and R-11.1 under the current 2015 method. Ask every bidder for the thickness-specific LTTR under S770-15 and the CCMC listing that publishes it, and the quotes become comparable.
Source: manufacturer TDS · CAN/ULC-S770
Does spray foam lose R-value over time?
Fresh closed-cell foam performs above its rated value, then declines over the first years as blowing agent in the cells trades places with air. LTTR already accounts for this: it is a five-year design value measured under CAN/ULC-S770, and building scientists treat it as representative of long-term service. So a foam rated R-11.1 LTTR at 2 inches is expected to deliver about that for the life of the assembly, not to keep dropping below it.
Source: CAN/ULC-S770-15 · buildingscience.com
What R-value does code require in Manitoba?
Manitoba builds to NBC 2020 Section 9.36 at Tier 1 (adopted January 1, 2024). In climate zone 7A, with the HRV Manitoba requires in new homes, the effective targets are RSI 8.67 (about R-49) for attics, RSI 2.97 (about R-16.9) for above-grade walls and RSI 2.98 (about R-16.9) for foundation walls. These are effective values, meaning thermal bridging through framing is counted, not just the insulation label.
Source: NBC 2020 Table 9.36.2.6 · M.R. 78/2023
What R-value counts for the Efficiency Manitoba rebate?
Only CCMC-published LTTR values count; declared or marketing R-values are rejected. The Home Insulation Rebate pays per square foot per R-value added: $0.03 for attics, $0.06 for wall cavities, $0.15 for exterior re-siding insulation and $0.06 for foundation walls, subject to a material-cost cap and eligibility rules. Pre-approval is required before work starts. The foam we install publishes its LTTR on CCMC listing 14133-L, so the rebate math is straightforward.
Source: efficiencymb.ca
Sources
Where these numbers come from
- CCMC evaluation 14133-L: National Research Council listing for the closed-cell foam we install, including the 50 mm design LTTR.
- CUSE Grizzly Gold technical data sheet, 2024 edition (thickness ladder under CAN/ULC-S770-15; superseded S770-03 value under "Other Properties"). Grizzly 005 TDS, 2021 (open-cell, ASTM C518).
- CAN/ULC-S770-15, Standard Test Method for Determination of Long-Term Thermal Resistance of Closed-Cell Thermal Insulating Foams.
- Building Science Corporation, High R-Value Wall Assemblies: Spray Foam Wall Construction: aged closed-cell range and whole-wall effective R analysis.
- Efficiency Manitoba, Home Insulation Rebate: rebate rates, pre-approval and the CCMC-LTTR requirement.
- NBC 2020, Section 9.36 and Table 9.36.2.6, as adopted by Manitoba Regulation 78/2023 (January 1, 2024).
Want the R-value math for your actual walls?
Every Ecologic quote states the thickness, the LTTR at that thickness, the test method and the code target. In writing, before you commit.