Graphite Garage Door Insulation: The Honest Facts

Home Materials & Product Comparisons Graphite Garage Door Insulation: The Honest Facts

July 31, 2025

Over the years, we heard the same question from a small but consistent group of customers: do you have anything cheaper? Something better than bare metal, but without the full investment of the composite system.

We took that question seriously. Graphite polystyrene was the obvious candidate — widely available in Australia, cheap to purchase from manufacturers, roughly 20% better thermal performance than plain white EPS, and a dark grey colour that gave it a premium look. We stocked it. We sold it as our ‘budget range’. It represented about 2% of our sales.

Then one afternoon, on an ordinary 30°C day, we left some panels in direct sunlight. What we photographed that day is further down this page. That photograph sent us to the peer-reviewed research. What we found confirmed what we had seen with our own eyes — and went further. This article is the result of that research.

Our conclusion: graphite polystyrene is not fit for purpose as garage door insulation in Australia. Not because it is a bad material. It is a good material in the right application. But a steel garage door in the Australian sun is not the right application. Here is the science behind that decision.

What is Graphite Polystyrene (GPS) Insulation?

Graphite polystyrene (also called GPS, graphite EPS, or graphite carbon polystyrene) is standard polystyrene foam with graphite particles added during manufacturing. The graphite helps slow down heat movement through the material, giving it roughly 20% better thermal performance than plain white polystyrene of the same thickness.

It is not a new product. GPS has been made in Australia for over 15 years and is widely used in walls, ceilings, and floors — where it is protected behind render, cladding, or plasterboard. Several large polystyrene manufacturers supply it across the country.

That is the honest truth: GPS is a good building material in the right application. The problem is that a garage door is not the right application — and here is why.

Several products in the Australian market are now claiming to be purpose-made garage door insulation. We look at what that term actually requires — and what it is currently being used to describe — in our article: Purpose-Made Garage Door Insulation in Australia.

The Problem Nobody Selling GPS Panels Tells You About

GPS Hits its Thermal Limit in a Steel Garage Door

The dark grey colour that makes GPS look sleek is caused by the graphite particles. Those same particles absorb heat from the sun extremely efficiently. In a wall, that is not a problem because the foam is hidden behind cladding. On a garage door, it is a serious issue.

According to peer-reviewed research published in Energies (Krause & Nowoświat, 2020), unprotected GPS panels exposed to solar radiation levels common in Australia reached their softening point of approximately 80°C under windless conditions. At radiation levels above 1,000 W/m², the panels physically deformed and melted.

Now consider this: a dark-coloured steel garage door facing the afternoon sun in an Australian summer regularly reaches 60–80°C on its surface. That heat conducts directly into any foam panel pressed against it.

The result: GPS installed on an Australian steel garage door is routinely exposed to temperatures at or above the point where the material begins to soften, warp, and fail.

By contrast, ThermaDoor is a purpose-built composite system that protects against this in two ways. The laminated Sisalation foil backing reflects radiant heat before it ever reaches the foam core, so the core never experiences the full surface temperature of the door. The engineered air cavity between the foil and the door skin keeps the two surfaces separated, preventing direct conductive heat transfer into the panel. Plain GPS has neither of these components.

These graphite EPS panels were photographed at our facility after being left in direct sunlight on a 30°C day — a completely ordinary Australian afternoon. This was not a controlled test. This was us watching our own stock deform before we had sold more than a handful of panels. The standard white EPS panel in the bottom right corner was left under identical conditions and is unaffected. This photograph is what sent us to the research presented in this article.

What Happens When GPS Gets Too Hot?

A four-year outdoor study by Nowoświat, Miros & Krause (2024), published in Sustainability, tracked what actually happens to GPS panels exposed to real-world conditions over time. The findings were clear.

The panels warped and fell off. GPS boards deformed so severely they detached from the surface they were fixed to.

Water absorption increased by 44%. Once the foam structure is compromised by heat, it absorbs significantly more moisture. In a garage environment, this means a higher risk of mould, rust on your door, and ongoing structural damage — directly undermining the “waterproof” claim made by some GPS sellers.

The insulating performance dropped. Once GPS is heat-damaged, its thermal conductivity increases by 8–10%, meaning it actually insulates worse than when it was new.

So, the product sold to you as waterproof, high-performing insulation becomes a moisture trap with degraded performance — all because of the Australian summer heat it was never designed to handle.

While researching the GPS category, we also looked at how these products were being marketed — and found several issues worth calling out:

1. The "Highest Thermally Rated" Claim — Without an R-Value

Some installers claim their graphite panels are the “highest thermally rated” garage door insulation on the market. Yet they refuse to publish a verified R-value.

In the insulation industry, R-values are the only standardised way to measure and compare insulation performance. Claiming to be the highest thermally rated without disclosing an R-value removes your ability to make an informed decision. It is like a car manufacturer claiming theirs is the fastest car while refusing to publish a top speed — the claim is meaningless without the number.

For a 25mm GPS panel glued or wedged directly to a steel door with no air gap and no reflective foil backing, the estimated R-value is approximately R0.95. That is a calculated estimate based on published thermal conductivity data and Australian Standard AS/NZS 4859.1 surface resistance values.

By comparison, ThermaDoor carries an independently verified assembly R-value of R1.43 (winter) / R1.39 (summer) — tested specifically for garage doors to AS/NZS 4859.2:2018. That is approximately 44% higher thermal performance than the estimated R-value of a GPS panel installed on the same door.

The gap comes down to composite technology. GPS is a single material. ThermaDoor is a four-component system: a thicker, denser EPS core that resists conducted heat in both summer and winter; a laminated Sisalation foil backing that reflects radiant heat before it reaches the foam; a purpose-built spacer system that maintains the air cavity the foil needs to function; and a UV-stable vinyl face that protects the assembly. Remove any one of those components and the R-value drops. GPS has none of them — making the “highest thermally rated” claim not just unverified, but fundamentally misleading about how insulation systems actually work.

Without an independently tested assembly R-value, any claim of being the “highest thermally rated” cannot be verified. Always ask for the engineering report.

2. The Soundproofing Myth

Some GPS installers also claim their panels will soundproof your garage or significantly reduce noise. This is not supported by acoustic science.

Blocking sound requires mass — heavy, dense materials that sound waves cannot pass through easily. GPS is extremely lightweight, typically weighing around 13.5 kg/m³. It is mostly air. Pressing a lightweight foam panel against a vibrating steel door does nothing meaningful to stop outside noise from entering.

While any foam will slightly muffle the metallic rattle of the door rolling up and down, that is not soundproofing. No STC or Rw acoustic rating is ever published by sellers making these claims, because the numbers would not support the marketing.

3. The "Lighter Colour" Naming Issue

One seller is known to be marketing a product under a name suggesting a lighter, “pearl-grey” version of graphite insulation.

Here is the thing: the dark grey colour of genuine GPS is a direct result of the graphite concentration required to give it better thermal properties. In my experience as a builder with over 45 years on the job, a lighter-coloured product likely contains less graphite (or none at all) and cannot offer the same performance.

Always ask to see the manufacturer’s technical datasheet before purchasing. If the seller cannot provide one, that tells you everything you need to know.

Is Graphite Polystyrene Thermally Rated for Garage Doors?

No. Plain graphite polystyrene is not thermally rated for garage doors. It does not carry a verified complete installed garage door assembly R-value under AS/NZS 4859.1 & 2:2018 — the standard required for accurate thermal modelling in a Home Energy Rating assessment.

For new builds and major renovations, plain GPS cannot be used by energy assessors as a credible input for garage door thermal performance under the National Construction Code (NCC) 7-star minimum requirements. Without a verified assembly R-value backed by an independent engineering report, the garage door defaults to an uninsulated value of R0.0 in the assessor’s software — regardless of what product is installed.

For existing homes, the same applies. The Australian Government’s Home Energy Rating pathway for existing homes (homeenergyrating.gov.au) identifies upgrade opportunities based on verified performance data. A GPS panel with no assembly R-value provides nothing an assessor can use.

ThermaDoor is the only garage door insulation product in Australia with independently verified dual-season complete installed assembly R-values — R1.43 winter and R1.39 summer, tested under AS/NZS 4859.1 & 2:2018 and supported by an independent engineering report. This is the only basis on which a garage door can be meaningfully included in a Home Energy Rating for either a new build or an existing home.

Learn more about garage door insulation and Home Energy Ratings →

Material R-Value vs Assembly R-Value: Why It Matters

When comparing garage door insulation, you need to understand the difference between two types of R-value.

A material R-value measures the foam on its own, sitting in a laboratory. It tells you nothing about how it will perform once installed in a steel garage door.

An assembly R-value measures the insulation as it actually works inside the complete door system — including the steel panels, air gaps, and any reflective foil. This is the number that matters for real-world performance.

Sellers of plain GPS typically quote material R-values (or no R-values at all), because their products have no foil backing and no verified assembly testing. The entire steel garage door acts as a thermal bridge that undermines the foam’s performance — and that is never reflected in a material-only figure.

Why Gluing Panels to the Door Makes Things Worse

One of the most common installation methods for GPS panels is gluing them directly to the garage door skin. This is a mistake for three reasons.

It removes the air gap. The small air cavity between the insulation and the door is a critical part of the thermal system. Remove it and you significantly reduce performance.

It traps condensation. Foam pressed hard against metal creates the perfect conditions for condensation, rust, and mould — especially in garages that swing between hot days and cool nights.

It impedes the door’s natural movement. Garage doors expand, contract, and flex with every cycle and temperature change. Gluing insulation into the door restricts that movement. AS/NZS 4505 sets out the performance requirements a garage door must meet — including safe and reliable operation. Any modification that impedes the door’s natural movement works against meeting those requirements. Panels cracking, falling out, or causing the door to bind are the predictable result.

Don't Forget the Spring Adjustment

During our time selling GPS panels, we also became aware of a safety issue that is rarely discussed by some sellers in this category.

Garage doors are precisely balanced. Add even a few kilograms of insulation and you can throw off that balance, putting extra strain on your motor and increasing the risk of the door failing to hold in the open position. AS/NZS 4505 requires that a garage door operates safely and reliably — adding weight without rebalancing the springs works against that. Always have a garage door technician check and adjust your springs after any insulation installation.

Some sellers of garage door insulation claim spring adjustment is unnecessary. This is incorrect and potentially dangerous. Regardless of how light an insulation product is, any addition of weight to a balanced mechanical system changes its operating load. A garage door spring that is out of balance does not just wear faster — it can fail suddenly, causing the door to drop without warning. No responsible installer should advise skipping a spring check after insulation is added to any garage door.

Why We Stopped Selling GPS — And Why We Only Make One Product

We did not discontinue graphite polystyrene because a competitor asked us to, or because it was cutting into our sales — it represented about 2% of our revenue. We discontinued it because we could not stand behind it.

A cheap product that does not work is not a budget option. It is just cheap.

ThermaDoor is a composite insulation system — meaning it combines multiple purpose-engineered components, each addressing a different mode of heat transfer, into a single assembly tested and verified as a whole. This is fundamentally different from any single-material product, no matter how good that material is on its own.

Every problem with GPS on a garage door — the heat vulnerability, the moisture absorption, the missing R-value, the lack of foil protection, the absence of a proper face — exists because GPS was never designed for this application. It was designed for walls and floors. ThermaDoor was designed specifically and only for garage doors, and every element of its construction addresses the exact problems GPS cannot solve.

The construction-grade EPS core is denser and more dimensionally stable than the SL Grade foam used in most GPS kits, giving it greater resistance to the physical stresses of a moving garage door.

The laminated construction-grade Sisalation foil backing — the same reflective foil used to wrap Australian homes — reflects radiant heat before it ever reaches the foam core. This is the critical layer GPS panels simply do not have. It also acts as a Class 2 vapour barrier, protecting against the condensation and moisture ingress that degrades GPS over time.

The laminated white vinyl face protects the foam from physical damage, makes the panel easy to clean, and gives it a professional finish that bare GPS foam cannot match.

And most importantly, ThermaDoor is the only Australian garage door insulation brand that publishes dual-season, independently verified assembly R-values — calculated specifically for garage doors to AS/NZS 4859.1 & 2:2018:

R1.43 (winter) / R1.39 (summer)

Not a material R-value. Not a guess. A verified, published number for the complete door assembly — so you can compare with confidence.

	GPS Panel (Glued to Door)	ThermaDoor Premium
Verified assembly R-value	None published	R1.43 (winter) / R1.39 (summer)
Foil backing (radiant barrier)	No	Yes — Class 2 Sisalation
Vapour barrier	No	Yes — Class 2
Protective face	Bare foam	Laminated white vinyl
Rated for garage doors (AS/NZS 4859.2)	No	Yes
Supports NCC & NatHERS compliance	No	Yes
Designed to move with the door	No	Yes
Thickness	Typically 25mm	35mm (30mm available for doors with a thinner panel profile)

To understand why ThermaDoor’s composite technology outperforms every single-material product on the market — read our full guide: Why Composite Garage Door Insulation Is the Only System That Works.

The Verdict: Ask for the Evidence

We still get asked for a cheap option. Our answer has not changed since the day we photographed those panels. ThermaDoor is a single product. Purpose-built composite technology. Independently verified. No budget line — because the only thing worse than no insulation is insulation that gives you false confidence while quietly failing.

GPS is a good insulation material in a wall, protected behind cladding, where it never sees direct heat. On an Australian steel garage door, the science informed our view: unprotected GPS is not suitable.

It softens in the heat. It absorbs moisture when it degrades. It has no foil barrier to reflect the radiant heat pouring off the steel. And the sellers promoting it as the “highest thermally rated” option cannot back that claim with a published, independently tested R-value.

If you want better than bare metal, this is it.

If you are comparing rubber sheets sold in black, read our guide to black garage door insulation and the installation factors to check before buying.

Download our Buyer’s Checklist and always ask for the evidence.

ThermaDoor is available as a DIY kit delivered to your door, or professionally installed by authorised distributors across Australia:

Want to know more about PIR as garage door insulation. Read our PIR vs ThermaDoor article.

Your Questions About Graphite Garage Door Insulation, Answered

Does graphite colour automatically mean better insulation?

Only marginally compared to plain white EPS of the same thickness. The graphite provides a small improvement in thermal performance, but true performance depends on thickness, density, air gap, and whether the product has a verified assembly R-value for garage doors.”

Why does GPS get so hot on a garage door?

The dark graphite particles that improve the foam’s insulating properties also absorb solar and radiant heat very efficiently. On a steel garage door that can reach 60–80°C in an Australian summer, that heat conducts directly into the foam, pushing it toward and beyond its softening point.

Do graphite garage door panels soundproof the garage?

No. GPS is extremely lightweight and cannot effectively block external noise. Genuine soundproofing requires heavy, dense mass. No seller of GPS garage door panels publishes an acoustic rating to support their soundproofing claims.

Is gluing insulation panels to the door a good idea?

No. Gluing removes the essential air gap, increases the risk of condensation and mould, and fights the door’s natural expansion and contraction. A spacer system should always be used.

For new home builds, does plain graphite insulation support 7-star NatHERS ratings?

No. Plain graphite polystyrene does not carry a calculated assembly R-value under AS/NZS 4859.1&2:2018 for garage doors and cannot be used for energy efficiency assessments. A purpose-built product with a verified assembly R-value is required.

What if I want the look of black panels and verified performance?

Currently, no plain black graphite panel on the market offers a verified assembly R-value and the durability of a laminated, foil-backed premium panel. If verified performance is your priority, choose a purpose-built system.

Ready to make your garage more comfortable?

Get exact DIY pricing online or find professional installation near you.

DIY kits ship Australia-wide · Professional installation available through authorised distributors

References and Further Reading

Bureau of Meteorology (BOM), Australian Government. Annual Climate Statement 2025. Published 9 February 2026. https://www.bom.gov.au/climate/current/annual/aus/

Bureau of Meteorology (BOM ), Australian Government. Rainfall and Temperature Records — Climate Extremes. https://www.bom.gov.au/climate/extreme/records.shtml

Lakatos, Á. & Csík, A. (2022 ). Multiscale Thermal Investigations of Graphite Doped Polystyrene Thermal Insulation. Polymers, 14(8), 1606. https://pmc.ncbi.nlm.nih.gov/articles/PMC9031919/

Krause, P. & Nowoświat, A. (2020 ). Experimental Studies Involving the Impact of Solar Radiation on the Properties of Expanded Graphite Polystyrene. Energies, 13(1), 75. https://www.mdpi.com/1996-1073/13/1/75

Nowoświat, A., Miros, A. & Krause, P. (2024 ). Change in the Properties of Expanded Polystyrene Exposed to Solar Radiation in Real Aging Conditions. Sustainability, 16(17), 7320. https://www.mdpi.com/2071-1050/16/17/7320

Kordun, O. I. (2015 ). The Influence of Solar Radiation on Temperature Increment of Sheet Steel Structures. Archives of Civil Engineering, 61(1). https://www.researchgate.net/publication/282588771

Gaspar, G. et al. (2024 ). The parking dilemma for solar-powered vehicles. PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC10909751/

Standards Australia. AS/NZS 4859.1:2018 — Thermal insulation materials for buildings: General criteria and technical provisions. https://store.standards.org.au/product/as-nzs-4859-1-2018

Standards Australia. AS/NZS 4505:2012 — Garage doors and other large access doors. https://store.standards.org.au/product/as-nzs-4505-2012

Australian Building Codes Board. National Construction Code — Energy efficiency and building fabric. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/13-energy-efficiency/part-132-building-fabric

Australian Government. Your Home — Insulation. https://www.yourhome.gov.au/passive-design/insulation

The Conversation. Where did southern Australia’s record-breaking heatwave come from? Published 26 January 2026. https://theconversation.com/where-did-southern-australias-record-breaking-heatwave-come-from-274417

Peter Hinton

Peter is a licensed builder with over 45 years of experience in the construction industry. In 2012, his expertise in energy efficient construction inspired the invention of ThermaDoor Premium garage door insulation - the original purpose made garage door insulation in Australia.

ThermaDoor is the manufacturer of the products discussed in this article and has a commercial interest in their sale. While every effort has been made to ensure the accuracy of the information presented, readers are encouraged to conduct their own research and consult qualified professionals before making purchasing decisions. All R-values cited are independently verified assembly R-values under AS/NZS 4859.1/.2:2018.

Door Size	Panels	Price (from)
Single Door	8 panels	From $330
Single Door (Large)	10 panels	From $380
Double Door	16 panels	From $660
Double Door (Large)	20 panels	From $760