The FMP Blog

Metal Building Insulation Guide For Commercial Projects

  • May 16, 2024

Surprisingly, the most essential part of a building’s structure isn’t visible to the naked eye.

In wooden structures, it’s tucked behind a layer of drywall. In metal structures, it’s behind steel panels.

We’re talking about insulation.

A building’s insulation adds longevity, durability, and efficiency to large-scale commercial structures.

It absorbs sound, seals off humidity and temperature leaks, and prevents pests and rodents from invading your building.

But which type of insulation is best for metal buildings?

Below, we’ll discuss eight of the most popular insulation types that you’ll hear your builder or contractor mention early in the construction process.

Table of Contents

1. What Is R-Value?
2. Spray Foam
3. Batt (Blanket)
4. Loose-Fill
5. Rigid Board
6. Double Bubble Foil
7. Vapor Barrier
8. Which Type of Insulation Is Best For Metal Buildings?

But First, What Is R-Value?

R-value is an important term to understand when choosing insulation.

An insulation’s R-value describes its thermal resistance per inch of material.

The higher an insulation’s R-value, the less heat it allows to pass through it. R-values typically range from 2.2–2.9 for loose fiberglass fill to 6–7 for closed-cell spray foam.

Remember, this is per inch.

Without high R-value insulation creating a barrier, metal buildings would become scorching hot and humid in the summer and cold during the winter.

Understandably, this can put excess strain on the HVAC system to maintain a steady indoor climate. Switching these heating and cooling systems into overdrive reduces the building’s energy efficiency.

Beyond the insulation’s R-value, a building’s climate control depends on a few factors:

  • The building’s U-value: How well the roof and side walls prevent thermal transmission
  • The presence of a vapor retarder (or barrier): Prevents moisture with extreme temperature fluctuations
  • The geographical area: The U.S. Department of Energy divides the country into climate zones with an ideal R-value assigned to each (i.e., the chilly northeast requires a higher R-value than the southern border)
  • The insulation’s thickness: Thicker or denser insulations resist heat flow more efficiently

Now that we’ve demystified R-values, let’s take a closer look at the most popular metal building insulations.

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Spray Foam

Technician spraying foam on ceiling of building

Spray foam insulation — or spray polyurethane foam (SPF) — is one of the more controversial insulation choices for metal buildings.

We’ll explain why in a moment.

Made from isocyanate (ISO) and polyol resin, this foamy chemical is sprayed directly onto metal wall panels in a thin, even layer. The foam gradually expands to up to 60 times its liquid volume and hardens in minutes.

The driving force behind spray foam’s popularity is its flexibility. Unlike blanket or board insulations, each spray foam application is simple to customize.

The 1200+ PSI spray gun propels the foam into the voids between purlins, girts, and bridging. Yet, the foam also expands into tiny nearby crevices and awkward-shaped panels. This creates a dense, leak-proof seal with no air gaps or entryways for conniving pests and insects.

The anti-foam crowd argues that spray foam insulations are a potential nightmare for metal structures. The high-temperature spray foam can cause condensation when applied directly to metal panels. The moisture trapped beneath the insulation could corrode the panels long-term.

But with proper installation and flashing techniques, spray foam is safe and one of the most reliable insulations for metal.

There are two types of spray foam insulation:


Open-cell spray foam has tiny openings or air-filled bubbles in each cell. This option is less dense, spongier, and more affordable than closed-cell foam. However, it also lacks the moisture-resistant vapor retarder to prevent leaks.

R-value: 3.6–3.9

Closed Cell

Closed-cell insulations are stiffer, thinner, and denser than the open-cell variety. This opening-free structure better controls heat flow and doubles as an efficient vapor barrier.

Though far pricier, it also has twice the R-value of open-cell foam. As a result, this insulation is popular for climate control and energy efficiency in pole barns, metal garages, and commercial metal structures.

R-value: 6–7

Batt (Blanket)

Batt — or blanket — insulation is the traditional insulation method that comes pre-cut and rolled up. These woven fiberglass sheets resemble wool and sit at about 3+ inches thick, easily filling the gaps between framing.

Blanket insulation tends to be budget-friendly, non-combustible, and widely available to both contractors and laypeople at home improvement stores.

But, in addition to climate control, batt is also known for its soundproof quality. The tiny glass shards absorb sounds in either direction, making batt an ideal choice if you run a noisy factory in a residential area.

Although batt is made of tiny glass strands, it’s not entirely immune to moisture. When exposed to water, the fiberglass can log moisture in its pores, creating a breeding ground for mildew and limiting its climate control.

Blankets with a waterproof laminate backing on one side are ideal for metal structures, as they’re less likely to get wet and develop mold. These backings create a seal along the metal panels to prevent rodents from burrowing deep within the fibers, too.

Here’s a closer look at the most common types of batt insulation:


Rockwool — or mineral wool — is a blend of slag and basalt melted into thick blankets or sheets. The noticeably stiffer mineral wool has a few significant benefits over fiberglass blankets:

  • Three times denser
  • Higher melting point (in case of fire)
  • Better at preventing mold growth

These features make Rockwool a better choice for exterior wall insulation.

R-value: 3.1–3.7


Fiberglass insulation is the classic batt method seen in residential and commercial structures. Its backing provides a natural mold resistance, it’s 25—50% cheaper than mineral wool, and it’s much easier to install.

Opposite of mineral wool, fiberglass is best for interior walls.

R-value: 3


Loose-fill — or blown-in — insulation is a blend of recyclable particles or pellets made from plastic, cellulose, mineral, paper, or foam.

When using materials like cellulose, a small amount of water is added to the particles. This moisture activates the adhesive characteristics of cellulose, allowing the pellets to stick to the panels when blown from a 100-foot hose attached to a blowing machine.

Like the ever-popular spray foam insulation, loose-fill excels in filling crevices and narrow corners in prefab steel buildings without disrupting the framing.

Unfortunately, it poses a few challenges as well. For one, this method relies on filling enclosed cavities, like the gaps between wall studs. It also absorbs moisture and is more expensive than the alternatives.

Loose-fill insulation systems come in several forms, including:

  • Rockwool
  • Fiberglass
  • Recycled newspaper
  • Cellulose

R-value: 2.2–3.8 (varies depending on manufacturer and material)

Related: Custom vs. Standard Metal Structures

Rigid Board

Rigid board insulation is a popular alternative to traditional fiberglass blankets and the often expensive spray foam systems.

Made from plastics like polystyrene, polyurethane, or polyisocyanurate, rigid foam boards are stiff yet thin (0.5–2 inches thick) and easy to secure between steel framing members when cut precisely.

They also fall into the category of “continuous insulation systems.” This insulation is gapless through all structural elements without thermal bridging when caulked or taped together.

In layman’s terms, that means the insulation creates a seal around the interior of the building, blocking off other structural elements that may allow heat to escape or enter — such as conductive steel purlins.

The stiffness and airtight seal make rigid board insulation the best choice for lining flat roofs. Its density makes for an ideal sound-dampener if you manage a metal office building in an industrial park full of heavy machinery.

Ask your contractor or project manager about local ordinances, too! For example, many states consider exposed foam boards a fire hazard, requiring a ½-inch layer of gypsum on top to act as a flame-retardant thermal barrier.

R-value: 3.2–7

Double Bubble Foil

Ceiling with double bubble foil

Double bubble foil — shortened to “bubble insulation” — is a more modern insulation option that’s picking up steam in recent years. This method features two layers of air bubbles in its polyethylene core clenched between reflective aluminum foil on either side.

Some argue it’s not so much insulation as it is a radiant barrier. Foils certainly excel in the thermal barrier department, reflecting sunlight and radiant heat away from the building and its conductive steel components.

In fact, some bubble foils can prevent UV damage and reflect as much as 95% of radiant heat, making it a long-term, energy-efficient solution.

However, while still hotly debated, this ultra-thin 1/4–5/16-inch protective layer has plenty more perks for commercial companies.

First, foils with <1 perm ratings count as full vapor barriers. This water-resistant surface holds off condensation, leaks, and the eventual corrosion of metal panels caused by excess moisture exposure.

But in addition to a slick surface that repels water and avoids mold growth, these foils also claim a Class A fire rating. So in the rare event of an equipment or chemical fire on-site, the risk of flames spreading is quite low.

On top of being covered by decade-long warranties, double bubble foil is one of the thinnest, most energy-efficient, non-toxic insulations available.

R-value: 1–10

Vapor Barrier

While not technically a type of metal building insulation, a vapor barrier — or vapor retarder — can add longevity to a commercial metal building. These thin, film-like foil or plastic sheets line the insulation and serve as a breathable barrier between the exterior and interior of the building.

Yet, they’re often misunderstood or confused for air barriers.

Vapor barriers don’t block airflow entirely. Nor do they stop water droplets from dripping through cracked roof panels.

Rather, they collect water vapor to evaporate instead of leak into the wall panels or cause mold or corrosion through condensation.

Of course, not all insulations will require an additional vapor barrier (i.e., spray foam).

However, if you do decide to install one, the industry standard is to install it on the “warm side.” This setup will prevent condensation build-up and largely depends on your geographical location.

Which Type of Insulation Is Best For Metal Buildings?

Like most things in construction, the answer is “it depends.”

We’ll change the question to, “when is each type of insulation best in a commercial metal building?”

Here’s a quick guide to help you decide:

Spray Foam

Spray foam is generally the best insulation for metal buildings, particularly closed-cell foam. While it’ll require a slightly higher budget, spray foam is easy to install in large or awkward-shaped spaces, has its own built-in vapor barrier, and creates an impenetrable airtight seal.

Batt (Blanket)

Batt insulation is the more traditional and affordable choice if you’d prefer to dedicate a bulk of the budget to customization options. Contractors suggest blanket insulation for retrofit projects, noise control, and basic metal builds.


Loose-fill insulation isn’t always the most logical choice for large-scale commercial metal structures. However, it’s a great addition to buildings with tight or narrow corners that make classic batt installation difficult.

Rigid Board

Rigid board insulation offers the perfect blend of soundproofing, vapor resistance, climate control, and continuous insulation. Given its thickness, rigid board has a high R-value, but it may require a gypsum board layer to abide by local building codes.

Double Bubble Foil

Double bubble foil excels in nearly every criteria. It repels moisture well, reflects up to 95% of radiant heat, and prevents mold and corrosion. Foil is the most reliable option for insulating metal buildings if the budget allows.

Related: How Insulated Metal Panels Are Used in Modern Construction


Each of these insulation types performs well, protects the building’s interior from radiant heat and moisture (to an extent), and adds a touch of energy efficiency to steel buildings.

However, the best option depends on your geographical location and construction budget.

The true best choice might be a combination of the insulation options reviewed above.

For instance, a combination of loose-fill and batt or closed-cell spray foam and double bubble foil could be more effective than any one option on its own.

If you’ve already hired a contractor or project manager, discuss your insulation options to find the one that best matches your future building best.

If you haven’t yet hired a contractor or project manager but you’re looking for one in Colorado, contact us today.

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