Understanding the differences between white EPS and graphite EPS (without getting the calculation wrong)
EPS lambda: what really changes between white and graphite
In ETICS, the declared lambda (λD) of expanded polystyrene directly determines R. White EPS is often around 0.038 W/m.K. Graphite EPS frequently drops to around 0.031 W/m.K. Base your calculations on the DoP for the installed board, not on an “average” value.
| Family | λD (W/m.K) | Thickness for R = 4.0 (mm) |
|---|---|---|
| White EPS | 0.038 | 152 |
| Graphite EPS | 0.031 | 124 |
EPS insulation: density, mechanical strength, and long-term performance depending on the application
Thermal performance says nothing about durability. For ETICS under render, decide based on the compression class, creep, and water absorption stated in the DoP, consistent with the board layout, fixings, and impact zones. Density alone is not enough.
Graphite EPS: when the performance gain is real on site
The gain is clear where thickness is constrained (window reveals, edges, supports) or if you want more R at the same thickness. It disappears quickly if joints are poorly butted, if fixing thermal bridges are underestimated, or if you calculate with the wrong lambda. To make your thickness and performance choices more reliable, use a thermal resistance calculator rather than rough estimates.
When expanded polystyrene is enough in ETICS under render: common cases and usual thicknesses
Most commonly installed ETICS thicknesses: practical benchmarks by thermal target
| R target (m².K/W) | White EPS thickness (mm) | Graphite EPS thickness (mm) |
|---|---|---|
| 3.7 | 140 | 115 |
| 4.5 | 170 | 140 |
| 5.0 | 190 | 155 |
On typical masonry (brick, blockwork, concrete), ETICS under render in expanded polystyrene works well in most configurations, as long as you stay within a complete ETICS system and treat the details properly.
ETICS under render: system compatibility and key points to watch during installation
Base the package on a complete system (ETE/DTA). Board layout, flatness, prescribed adhesive pattern, mechanical fixing, and mesh embedding under the render must follow the system documentation. During installation, secure the base level at plinth, the reveals, sills, and slab edges. To go further on these sensitive areas, rely on singular details. Avoid any solvent-based product that is incompatible with EPS.
Choosing between white EPS and graphite EPS: balancing performance, thickness, and facade details
| Product | Typical lambda (W/m.K) |
|---|---|
| White EPS | 0.038 |
| Graphite EPS | 0.031 |
Graphite reduces thickness for the same R value. You gain on façade details (insulation returns, window alignment, accessories). In return, protect the boards from the sun before the base coat and render, and recheck the usable length of the fixings.
When EPS is ruled out: the 3 limits you need to know before proposing your solution
Fire performance: site constraints and specifications to check (ETICS, public buildings, residential)
Expanded polystyrene remains a common ETICS insulation, but it becomes unsuitable as soon as fire requirements call for a more favourable facade reaction-to-fire performance. In public buildings and high-rise buildings, check the applicable requirements, the reaction-to-fire classification of the complete system (insulation + base coat + render), and any fire barriers. Without these documents, you cannot justify the solution in an inspection.
Rodents: risk areas, essential protections, and common mistakes
EPS is vulnerable at the base of the facade, behind open-jointed cladding, and in agricultural or wooded areas. If the job does not allow durable protection, switch insulation families or reinforce the detail. Costly mistakes include: stopping the render too high, no proper starter track, and open singular details.
Solvents and incompatible products: adhesives, sealants, cleaners, and degradation risks
Some solvents soften or dissolve EPS. Avoid adhesives, primers, sealants, and cleaners based on organic solvents. Stick to system-compatible ETICS products that are documented and traceable. Cleaning with the wrong product can cause an irreversible loss of thickness even before the render is applied.
Make a quick decision at quotation stage: a simple method to choose EPS, graphite EPS… or another insulation
Quick reading of technical datasheets: EPS lambda, fire class, compressive strength
When quoting, keep 3 values. Lambda (performance), Euroclass (reaction to fire), and CS(10) (compression). Expanded polystyrene comes in white and graphite versions. Do not mix them up.
| Product | Lambda (W/m.K) | Euroclass | CS(10) (kPa) |
|---|---|---|---|
| White EPS (common ETICS under render) | 0.036 to 0.038 | E | 70 to 100 |
| Graphite EPS (common ETICS under render) | 0.030 to 0.032 | E | 70 to 100 |
Edge cases: plinths, exposed areas, and details that can tip the balance
Three quick triggers. Fire if an A1 requirement applies, or fire barriers to be provided depending on the system. Rodents at the foot of the facade and behind open protective elements. Solvents and bituminous products. Do not use solvent-based adhesives or coatings in contact. At plinth level, switch to an insulation designed for moisture and impact, or specify continuous mechanical protection.
2026 checklist to secure your choice: manufacturer requirements, standards/assessments, insurance
- Product identified in the quotation. Type, thickness, lambda, CS(10), Euroclass, CE marking, and ACERMI if required.
- ETICS system covered. Technical assessment, DTA or ETA. Fixings and base coat compliant with the document.
- Job traceability. Batches, substrate acceptance reports, and consistency with your ten-year liability insurance.
Installer questions: direct answers about expanded polystyrene in ETICS
Can you mix white EPS and graphite EPS on the same facade?
Yes, but only if you stay within the same ETICS under render system (same adhesives, same fixings, same render, same accessories). Avoid random mixing. Lay out by clear zones, keep the same thickness on one plane, and pay attention to the transition (staggered joints, straight edges, no “steps” that show through the finish).
What is the impact of lambda on thermal bridges and window reveals?
| Insulation | Lambda (W/m.K) | Thickness for R 4 (mm) |
|---|---|---|
| White EPS (order of magnitude) | 0.038 | 152 |
| Graphite EPS (order of magnitude) | 0.031 | 124 |
The lower the lambda, the more usable thickness you gain in the reveals. In practical terms, it makes the insulation return and the adjustment of extensions easier, without creating a thermal weak point at the frames. For more detail, see thermal bridges and how to treat them.
What should you do in renovation when thickness is limited: graphite EPS or another option?
If the constraint is “a few centimetres,” graphite expanded polystyrene is often the first lever. Switch to another solution if the context imposes stronger fire requirements, if the rodent risk is high without suitable protection, or if you are exposed to incompatible solvent-based products. When every millimetre counts, move to a more high-performance insulation only within a compatible system covered by a Technical Assessment.
