Spray Foam Breaks Down in Humidity.

Spray Foam Breaks Down in Humidity.

Spray Foam Breaks Down in Humidity. 

Spray foam insulation is often sold as a permanent solution: seal everything, lock out moisture, forget about it forever.

That promise only holds up in one place:

The brochure.

In hot–humid climates like Atlanta, spray foam isn’t operating in ideal conditions. It’s operating under constant moisture load, heat, and pressure cycling—the exact combination that stresses polyurethane plastics over time.

And yes: spray foam can and does break down in humidity.

Not dramatically.
Not overnight.
But quietly, chemically, and expensively.

What “Breakdown” Actually Looks Like (Because It’s Not a Cartoon)

Spray foam doesn’t usually collapse or melt. The failures are subtler—and worse:

  • Loss of adhesion to framing or sheathing

  • Shrinkage or pulling away

  • Softening or embrittlement

  • Persistent or returning odors

  • Declining air-sealing performance

  • Hidden moisture accumulation behind the foam

These failures often appear years after installation, when warranties are hard to enforce and remediation means demolition.

That’s not resilience.
That’s fragility on a delay.

The Chemistry Problem No One Likes to Talk About

Spray foam is a polyurethane plastic. Polyurethanes are well known in materials science to be vulnerable to hydrolysis—a moisture-driven chemical breakdown process accelerated by:

  • Heat

  • Humidity

  • Time

Atlanta supplies all three, relentlessly.

High humidity doesn’t need to soak spray foam to cause problems. Repeated exposure to moisture vapor, combined with thermal cycling, is enough to degrade performance over time.

This isn’t controversial chemistry.
It’s baseline polymer behavior.

Installation Conditions Matter — and Atlanta Rarely Cooperates

Spray foam manufacturers specify narrow windows for:

  • Substrate moisture

  • Ambient humidity

  • Temperature

  • Ventilation

  • Cure time

Those aren’t suggestions. They’re guardrails.

In real Atlanta construction conditions:

  • Humidity fluctuates rapidly

  • Substrates hold moisture

  • Attics and crawlspaces run hot

  • Jobs are scheduled for speed, not chemistry

When foam is sprayed outside ideal conditions, incomplete curing and trapped moisture become long-term liabilities embedded inside the building envelope.

You don’t see the problem right away.
You inherit it later.

Closed-Cell Foam Can Make Moisture Problems Worse

Closed-cell spray foam is marketed as a moisture solution because it resists vapor diffusion.

In humid climates, that can backfire.

When moisture gets into an assembly—through leaks, diffusion, or construction moisture—closed-cell foam can:

  • Prevent drying

  • Trap moisture against wood

  • Hide rot and decay

  • Delay detection until damage is advanced

The foam can look “fine” while the structure behind it deteriorates.

That’s not protection.
That’s concealment.

Heat Accelerates Everything (Especially in the South)

Plastics age faster in heat.
That’s not opinion — it’s physics.

Atlanta’s long cooling season and hot roof decks:

  • Speed up chemical aging

  • Reduce flexibility over time

  • Increase brittleness and adhesion loss

What performs acceptably in cooler, drier climates often ages prematurely here.

Spray foam doesn’t fail because it’s “bad.”
It fails because it’s chemically sensitive in a chemically aggressive environment.

Compare That to Materials That Expect Moisture

Hemp insulation and sheep’s wool don’t try to deny moisture exists.

They:

  • Absorb and release humidity safely

  • Remain stable when moisture is present

  • Do not rely on chemical curing

  • Do not trap water in assemblies

  • Do not degrade due to humidity exposure

They fail gracefully, dry naturally, and continue functioning in variable conditions.

That’s not nostalgia.
That’s appropriate material selection.

The Real Issue Isn’t Spray Foam — It’s Overconfidence

Spray foam demands:

  • Perfect chemistry

  • Perfect conditions

  • Perfect installation

  • Permanent perfection

Atlanta doesn’t offer that.

Homes are not labs.
Climate is not controllable.
Moisture always finds a way.

When systems are fragile, they eventually fail.

The Bottom Line

You can say this honestly and accurately:

Spray foam is chemically sensitive to humidity, and in hot–humid climates it can degrade, lose adhesion, and create long-term moisture and performance problems—especially when installation conditions aren’t perfect.

That’s not fear-mongering.
That’s reality-based building science.

Atlanta doesn’t reward materials that need everything to go right forever.

It rewards materials that can adapt, breathe, and recover.

Back to blog