Avoid moisture, mould and compliance risks by avoiding open cell insulation in garage doors. 

When insulating your garage, not all products are created equal. Many homeowners, and even some installers, mistakenly turn to open cell insulation in garage doors, like polyester or fibreglass batts. These materials work well in walls and ceilings, but they can cause serious issues when applied directly to metal sectional garage doors, especially in Australia’s climate.

Let’s explore why open cell insulation isn’t suitable for garage doors, and what compliant, purpose-built alternatives like ThermaDoor Premium range offer instead.

What Is Open Cell Insulation in Garage Doors?

Open cell insulation includes materials like:

• Polyester batts

• Fibreglass batts

• Acoustic wall panels

These products trap air to reduce heat transfer and made to be used in lined, enclosed spaces such as walls, ceilings, and floors. But they are not designed for direct contact with metal, moisture, or extreme outdoor temperature changes. This makes them unsuitable for garage doors.

Manufacturer Warnings Are Clear

Most open cell insulation products include warnings in their technical datasheets, such as:

“Not recommended for direct exposure to moisture or unlined metal surfaces”.

“Use a protective barrier when adjacent to metal cladding to avoid condensation”.

“Do not use where the product will contact water or high humidity”.

“Not recommended for visual applications as the surface may show creases, wrinkles or slight colour variations”.

These statements are based on known risks. Yet they’re often overlooked when installing insulation into garage doors.

The Risks of Using Open Cell Insulation on Garage Doors

Metal garage doors are prone to temperature fluctuations, condensation, and moisture exposure. Installing polyester or fibreglass batts directly against the door skin can lead to:

1. Condensation & Moisture Buildup

Moisture collects easily on cold metal. Without an air gap, open cell materials trap this moisture, risking rust and deterioration of the garage door.

2. Mould Growth Over Time

While polyester resists mould better than some materials, trapped moisture still leads to long-term issues, especially in coastal or humid regions.

3. Reduced Insulation Performance

Direct contact between insulation and metal can cause thermal bridging, allowing heat to transfer through the door.

4. Waterlogging & Sagging

Without a water-resistant barrier, these materials can absorb moisture, becoming heavy and ineffective.

5. Unverified R Values

The stated R values of polyester or fibreglass are tested for walls and ceilings, not garage doors. Using them for doors can result in inaccurate star ratings and non-compliant energy assessments.

Installation Alignment: AS3999

According to AS 3999 (Bulk Thermal Insulation – Installation):

Insulation should not be installed directly against unlined metal surfaces.

Best practice requires a separation layer or cavity to prevent:

• Condensation damage

• Rust and corrosion

• Poor thermal performance

If your current garage insulation doesn’t comply with AS 3999, it could lead to damage and safety issues.

The Better Choice: ThermaDoor Premium Garage Door Insulation

Unlike open cell options, ThermaDoor Premium Range is purpose-built for Australian garage doors. It’s designed to perform under harsh conditions, comply with national standards, and protect your door long-term.

Key Benefits:

• Water-resistant laminated finish – Blocks moisture and prevents sagging

• R1.48 tested thermal performance – Real results on real garage doors

• Impact-resistant and pet-proof – Durable for everyday garage use

• Built-in air cavity design – Aligns with AS 3999 for maximum thermal efficiency

• Available as DIY or professional install – Trusted by builders, architects and homeowners Australia-wide

The Bottom Line: Don’t Risk It With Open Cell Insulation

If you’re wondering how to insulate a metal garage door properly, the answer is clear:

❌ Don’t use wall batts, fibreglass, or polyester designed for enclosed interior spaces

✅ Choose a compliant, purpose-built insulation system like ThermaDoor Premium

With ThermaDoor, you’ll get:

• Better energy efficiency

• Longer product life

• Safer installation

• Confidence in your home’s compliance