Insulated Container R-Value Comparison Canada 2026

By Paul LeBlanc, owner, and Christian LeBlanc, second-generation operator, Van Blanc Ent. Inc.

Insulation is the single decision that decides whether your container is comfortable, dry, and useful through an Ontario winter, or whether it sweats, rusts, and freezes in February. The R-value-per-inch number on the spec sheet is only half the story. The other half is moisture, air sealing, and how the chosen product behaves against a corrugated steel wall that conducts heat 200 times faster than the wood-framed wall most insulation products were designed for.

Van Blanc has supplied shipping containers in Ontario since 1995. Roughly two thirds of the containers we sell get insulated at some point in their service life, whether as a workshop, hunt camp, off-grid cabin, kennel, grow room, or conditioned storage. We see the consequences of every insulation choice come back through customer phone calls 18 months later. This guide is the honest comparison, with the moisture caveats that most spec-sheet articles skip.

Which Insulation Gives the Best R-Value Per Inch in a Container?

R-value is a measurement of resistance to heat flow. Higher R is better. The R-value of an insulation assembly is the product per inch multiplied by the actual installed thickness, not the wishful thickness. The values below come from the manufacturer data sheets and from the testing summarized by R-Value Associates and the Canadian Home Builders’ Association reference tables, evaluated at the standard 75 degrees Fahrenheit test temperature.

• Closed-cell spray polyurethane foam (ccSPF): R-6.5 to R-7.0 per inch. Density roughly 2 pounds per cubic foot. Two-component spray applied at 1 to 2 inch lifts. Bonds to steel.
• Polyiso rigid panel (polyisocyanurate): R-6.0 to R-6.5 per inch at lab temperature. Drifts to R-5.0 to R-5.5 per inch at 0 degrees F, which Ontario sees most winter nights.
• XPS rigid panel (extruded polystyrene): R-5.0 per inch. Pink, blue, or green sheets. Holds R-value across temperature range better than polyiso.
• EPS rigid panel (expanded polystyrene): R-3.6 to R-4.2 per inch. White, beadboard-textured panels. The lowest R per inch of the rigid foams but the cheapest per board foot.
• Open-cell spray polyurethane foam (ocSPF): R-3.5 to R-3.7 per inch. Density roughly 0.5 pounds per cubic foot. Absorbs water. Do not use against steel.
• Fiberglass batt: R-3.0 to R-3.5 per inch. The standard wood-frame wall insulation. Cheapest per square foot. Major caveats for containers covered below.
• Mineral wool batt (Rockwool): R-4.0 to R-4.2 per inch. More dimensional stability than fiberglass, better moisture handling, but still not a vapor or air barrier.

Paul LeBlanc, our owner, has 40 years in the trade and 30 years selling containers. “R-value-per-inch is the headline. But for a steel container in Ontario, the question that decides comfort is not what R-value you bought, it is whether your assembly stops warm interior air from hitting the cold steel wall and condensing. Closed-cell foam wins not because it has the highest R, but because it solves both problems with one product.”

For a broader walkthrough of insulating shipping containers in Ontario, see our insulated shipping containers Ontario hub.

Closed-Cell Spray Foam: The Gold Standard for Containers

Closed-cell spray polyurethane foam is the highest-performing insulation per inch of wall depth available for shipping container retrofits. Two components (an A-side and a B-side) are mixed at the spray gun, applied wet to the inside face of the corrugated steel, and cure to a rigid closed-cell foam within seconds. Cured foam is roughly 2 pounds per cubic foot, structurally rigid, and bonded to the steel.

What closed-cell foam does for a container that no other insulation product does in one step:

• Air seals. Cured ccSPF at 1 inch is an air barrier per the National Building Code definition. Air leakage is the dominant heat loss path in a poorly sealed container, often larger than conduction through the walls.
• Vapor retards. ccSPF at 2 inches or more is a Class 2 vapor retarder, which means warm interior moisture cannot diffuse through the foam to hit the cold steel and condense.
• Bonds to steel. Once cured, the foam is structurally fused to the corrugated profile. There is no gap behind it where moisture can settle.
• Fills the corrugation. Rigid panels need furring strips to bridge the corrugated profile of the steel wall. Foam fills the corrugation channels directly, which adds usable interior space and continuous R-value.
• Adds structural rigidity. A container insulated at 2 inches of ccSPF gains noticeable wall stiffness, which matters for the longer 40 foot units where wall flex can rattle through doorways.

The R-value math for closed-cell on a container in southern Ontario looks like this: 2 inches gives you R-14, which is below the practical target. 3 inches gives you R-21, which meets the R-20 minimum wall target and leaves room for a small thermal break gain at studs. 4 inches gives you R-28, which is what we recommend on the ceiling where heat loss is highest. The pricing reality is that ccSPF is priced per board foot installed in Ontario (one board foot is one square foot at one inch thick), so 3 inches across a 20 foot container interior is a meaningful professional installation; ask us for a current rate.

Closed-cell is the only insulation we recommend without a long list of caveats. The caveats it has are real but narrow: it must be installed by a licensed sprayer using current low-GWP blowing agents (most Canadian installers switched to HFO blowing agents by 2024, which dropped the global warming potential by roughly 99% versus the old HFC-245fa formulations), and the installer must verify the substrate is dry and above the manufacturer minimum temperature, which is typically 40 to 50 degrees F.

For ceiling-specific guidance where heat loss is highest, see our container modifications in Ontario guide.

Open-Cell Spray Foam: Wrong Tool for Steel Walls

Open-cell spray polyurethane foam (ocSPF) is half the density of closed-cell and roughly half the R-value per inch. In a wood-framed wall it has legitimate uses: it air seals, it allows seasonal drying back into the building, and it costs less per board foot than closed-cell.

Against a corrugated steel container wall, those advantages flip into a problem. Open-cell foam is moisture permeable, which means interior humidity diffuses through the foam during heating season and hits the cold steel skin. Behind the foam, against the steel, there is no place for that moisture to go. It accumulates, freezes, thaws, and starts a rust cycle on the inside face of the container that you cannot see without cutting the foam open.

This is not a theoretical risk. We have inspected three customer containers over the last seven years that had open-cell foam installed by a residential sprayer who did not understand the steel-wall application. All three showed visible interior rust within 24 months. One needed a partial wall replacement at the bottom of two side panels.

The Sprayman insulation knowledge base, the Building Science Corporation white papers on metal building insulation, and every reputable container conversion specialist we know all say the same thing: do not use open-cell against steel. Closed-cell or rigid panels with a proper vapor barrier are the only sound options. Use ocSPF on a wood-framed addition or interior partition inside the container, but not against the container shell.

For the underlying physics of why steel walls drive condensation, see our shipping container condensation Ontario guide.

Rigid Foam Panels: XPS, Polyiso, and EPS

Rigid foam panels are the budget-friendly DIY alternative to spray foam. You buy 4 by 8 foot sheets at a building supply, fur out the corrugated wall with treated wood strips, cut the foam to fit between the furring, seal the seams with foil tape or canned foam, and add an interior wall finish over the assembly. Three rigid foam chemistries dominate the Ontario market.

Polyiso (polyisocyanurate) is the highest R-value rigid foam at room temperature, rated R-6.0 to R-6.5 per inch. It is faced with foil on both sides, which acts as a radiant barrier in cavity assemblies. The polyiso catch is thermal drift in cold weather: the R-value drops to roughly R-5.0 to R-5.5 per inch at 0 degrees F because the low-conductivity blowing agent inside the cells condenses. Ontario sees 0 F or colder on roughly 20 to 30 nights per winter in Brantford and on many more in northern Ontario. The honest design number for a polyiso container wall in southern Ontario is R-5.5 per inch, not the R-6.5 on the package.

XPS (extruded polystyrene) is the pink, blue, or green sheet most contractors recognize as Dow Styrofoam, Owens Corning Foamular, or Kingspan GreenGuard. It is rated R-5.0 per inch and holds that value across temperature range better than polyiso. XPS is moisture stable and rated for ground contact, which makes it the right choice for the container floor and any wall section near the floor where moisture splash is a concern. XPS is the most predictable rigid foam choice for an Ontario container.

EPS (expanded polystyrene) is the white beadboard panel, often used as foundation insulation or under concrete slabs. Rated R-3.6 to R-4.2 per inch depending on density (Type I is the cheapest and lowest R, Type IX is denser and higher R). EPS is the cheapest rigid foam per board foot, but the R per inch is the lowest, which means you need more wall depth to hit the R-20 target. EPS does not absorb water in liquid contact but is more vapor permeable than XPS or polyiso, which can be either an advantage or a problem depending on the rest of the assembly.

The rigid foam install on a container is more labor than spray foam because of the furring strips and the seam sealing. Done well, with continuous seam tape and a separate interior vapor barrier installed warm-side, rigid foam can perform within 80 to 90 percent of a spray foam assembly. Done poorly, with gaps at the corrugation channels and untapped seams, the actual assembly R drops far below the panel rating because air leakage bypasses the insulation entirely.

For full conditioning context including how rigid foam pairs with mini-split heat pumps, see our container HVAC Ontario guide.

Fiberglass Batt: Why It Does Not Fit Containers Well

Fiberglass batt is the pink or yellow fluffy insulation most homeowners have seen in a wood-framed wall. Rated R-3.0 to R-3.5 per inch, it is the cheapest insulation by board foot of anything on this list. Why we rarely recommend it for a container:

• It needs a cavity. Fiberglass batt only performs at its rated R-value when it fills a sealed cavity at the correct compression. The corrugated steel wall of a container is not a cavity. To install batt, you must build a full secondary stud wall inside the container, which costs you 3.5 to 5.5 inches of interior space along every wall plus the labor of building a code-correct stud assembly.
• It is not an air barrier. Fiberglass batt does not stop air movement. Without a separate continuous air barrier on the warm side, interior heated air drives straight through the batt to the cold steel wall, carries moisture with it, and condenses on the steel. Result is the same as open-cell foam: hidden rust.
• It absorbs moisture. Wet fiberglass loses most of its R-value and stays wet for weeks. In a container where condensation is the dominant moisture risk, a soaked batt is worse than no insulation at all because the steel cannot dry behind it.
• Compression destroys R-value. Stuffing a batt into the corrugation channels to fill the gaps compresses the fibers and drops the rated R. The product only works at its uncompressed thickness.

Fiberglass batt has one valid use in a container: as a fill between secondary studs on top of a continuous closed-cell foam or rigid panel layer. The foam against the steel handles air sealing, vapor control, and the first 70% of the R-value. The batt in the secondary cavity adds the remaining R without exposing fiberglass to the moisture risk. This is called a hybrid assembly and is the highest-performance container insulation we install, but it costs more than straight closed-cell because you are paying for both layers.

Brantford and most of southern Ontario sits in Zone 5 (4,000 to 5,000 heating degree days). Toronto, Hamilton, and the Niagara region are in the same zone. Ottawa, North Bay, and the Muskokas are Zone 6 (5,000+ HDD). Northern Ontario is Zone 7. The OBC minimums for residential walls in Zone 5 are R-22 effective, and Zone 6 is R-24 effective. Ceilings are R-60 in Zone 5 and Zone 6 under SB-12.

A shipping container is not a code-built residential building, so SB-12 does not strictly apply to a container used as a workshop, storage building, or detached studio. But the Ontario climate physics do apply. If you heat a container through a southern Ontario winter without hitting roughly R-20 walls and R-30 ceiling, you will be running a heat source non-stop in January and your heating cost will exceed what the container is saving you in rent or workspace.

The practical insulation thickness math for a single 20ft container in Brantford to hit those targets:

• Closed-cell spray foam: 3 inches walls (R-21), 4 inches ceiling (R-28). Closest practical target.
• Polyiso rigid panel: 4 inches walls (R-22 nameplate, R-19 to R-20 cold-derated), 5 inches ceiling (R-26). Practical target with derating.
• XPS rigid panel: 4 inches walls (R-20), 6 inches ceiling (R-30). Hits target without derating.
• EPS rigid panel: 5 inches walls (R-20), 7 to 8 inches ceiling (R-28 to R-32). Hits target but loses interior space.
• Hybrid (2 inch ccSPF plus 3.5 inch batt on secondary stud): Walls R-26 plus, ceiling R-30 plus. Highest performance.

For an unheated storage container or one used only seasonally May through October, the case for insulating at all is weaker. Many of our customers use uninsulated containers for tool and seasonal storage with no comfort or condensation issues because the container is not heated above the dew point of the outside air.

Cost Per Square Foot, Installed

The honest installed cost per square foot in Ontario in May 2026, including both materials and labor where applicable, runs roughly as follows. These ranges shift with installer, location, and current foam chemistry pricing, but the bands are realistic across our supplier network:

• Closed-cell spray foam, 3 inches installed: the highest per-square-foot figure of the wall options. Professional spray crew only.
• Polyiso rigid panel, 4 inches installed by DIY: a mid-range per-square-foot figure including foil tape, furring, and seam sealing. Paid labor adds to that.
• XPS rigid panel, 4 inches installed by DIY: a mid-range per-square-foot figure. Paid labor adds to that.
• EPS rigid panel, 5 inches installed by DIY: the lowest per-square-foot material figure of the rigid foams, but most interior space lost.
• Fiberglass batt with secondary stud wall and air-barrier membrane: low per-square-foot material cost including the stud wall lumber, but the highest labor and space penalty.
• Hybrid (1 to 2 inch ccSPF plus batt fill): the top of the per-square-foot range. Highest performance, highest cost.

For a single 20ft container with roughly 600 square feet of wall, ceiling, and floor surface to insulate, the all-in installed cost runs from the low end (a budget EPS DIY job) up through a mid-range closed-cell professional install to the high end (a premium hybrid professional install). Most customers we ship to land in the middle with a 3 inch closed-cell professional install on walls and ceiling and rigid XPS on the floor. Ask us for a current rate.

Moisture Management: The Vapor Barrier Reality

In a heated Ontario container, interior air at 21 degrees C and 40% relative humidity has a dew point of roughly 7 degrees C. The container steel wall in January is at roughly the outdoor air temperature, which is well below that dew point on every cold day. Without a vapor retarder and air barrier, the warm interior air finds the cold wall, deposits moisture as condensation, and the wall stays wet until spring.

Closed-cell spray foam at 2 inches or more is its own Class 2 vapor retarder and air barrier, so no separate barrier is needed. This is the cleanest assembly and the reason ccSPF is the most foolproof container insulation.

Rigid foam panel assemblies need a separate continuous air barrier on the warm side of the insulation, plus careful seam sealing on the rigid panels themselves. The standard approach is 6 mil polyethylene sheet acoustical sealant-taped to the wall framing and to itself at all seams, then drywall or wood paneling over the poly. Foil-faced polyiso with foil-tape-sealed seams can serve as its own air barrier and vapor retarder if installed continuously, which is the cleanest rigid panel detail.

Fiberglass batt assemblies need both an air barrier and a vapor retarder, separately installed. This is where DIY fiberglass installs in containers most often fail: the batt is installed but the air and vapor control layers are not, and moisture finds the steel anyway.

The principle is that in Ontario heating climate, warm side gets the air and vapor control. Cold side breathes. Reverse that and the wall fails.

Why We Recommend Closed-Cell for Ontario Containers

If a customer calls us and is going to heat their container above outdoor temperature for any meaningful part of the year, we recommend closed-cell spray foam at 3 inches on walls and 4 inches on the ceiling. The reasoning is not “highest R per inch”, although it is. The reasoning is that closed-cell delivers four things in one product that any other assembly requires separate installation steps to achieve: continuous insulation, continuous air barrier, continuous vapor retarder, and direct steel bond with no gap behind the insulation.

Every container insulation failure we have inspected has been an assembly failure, not a product failure. Open-cell foam against steel. Fiberglass batt without an air barrier. Rigid foam with untapped seams. The steel container wall is unforgiving of installation shortcuts in a way that a wood-framed wall is not, because there is no sheathing layer to absorb minor moisture excursions. Closed-cell is the assembly that is hardest to mess up at the installation stage.

Paul’s plain-language summary: “If you are going to live in it, work in it through winter, or store anything that cares about humidity, pay for closed-cell. If you are using the container as cold storage May to October, leave it uninsulated. Anything in between, do rigid foam and pay attention to the seams and the air barrier or pay us to refer you to a foam crew. The middle path of fiberglass batt against a steel wall is the one we have to come fix later.”

For homes specifically, where the building science is most demanding, see our our guide to container home. For workshops where the conditioning needs are more flexible, see our container workshop Canada guide.

Frequently Asked Questions

Sources and Further Reading

• R-Value Associates, spray foam R-value per inch comparison chart and testing methodology
• Johns Manville, Spray Foam: Open-Cell vs Closed-Cell technical bulletin
• Rmax, rigid insulation R-value per inch reference for polyiso, XPS, and EPS
• NAIMA Canada, thermal requirements and Ontario climate zone reference data
• ArmorThane, closed-cell versus open-cell spray foam R-value technical guide
• Natural Resources Canada, Keeping the Heat In: insulation and air barrier guidance
• Building Science Corporation, air flow control in buildings and metal-skin moisture management