At Qomaira, we leverage advanced engineering simulation to solve complex design challenges. A critical question in building design, especially for fire-rated partitions, is the choice of insulation. Today, we’re diving deep into a comparative analysis of two common materials: Expanded Polystyrene (EPS) and Rockwool.
We used Computational Fluid Dynamics (CFD) and analytical methods. We modeled a standard 3-layer fire-rated wall. This helped us understand how each insulation performs under extreme heat. This isn’t just about theory; it’s about providing data-driven insights for safer, more efficient buildings.
The Two Contenders: A Quick Overview
We analyzed two identical wall assemblies, differing only in the insulation core:
- Scenario S1: Features a 50mm core of Expanded Polystyrene (EPS).
- Scenario S2: Features a 50mm core of Rockwool.
The rest of the wall assembly had a 5mm Magnesium Oxide (MgO) board on the exterior. A 150mm concrete block was on the interior. This was exposed to a severe fire temperature of 1500K (1227°C).
| Layer | 1st Scenario (EPS) | 2nd Scenario (Rockwool) |
| Outer Layer | Magnesium Oxide (MgO) Board (5mm) | Magnesium Oxide (MgO) Board (5mm) |
| Insulation | Expanded Polystyrene (EPS, 50mm) | Rockwool (50mm) |
| Inner Layer | Concrete Block (150mm) | Concrete Block (150mm) |
Our Methodology: CFD & Analytical Validation
To ensure accuracy and depth, we employed a multi-faceted engineering approach:
- Advanced CFD Simulation: Using ANSYS Fluent, we created a 3D finite volume model to capture transient heat transfer, including effects of radiation and precise material properties.
- Lumped Capacitance Method (LCM): An analytical model was used to validate the CFD results and provide a theoretical baseline for temperature rise.
- Compliance Benchmarking: Results were rigorously checked against key international standards: BS EN ISO 1182:2020 (non-combustibility) and NFPA 251 / ASTM E119 / UL 263 (fire resistance of building constructions).
Key Findings: A Tale of Two Insulations
Our simulations revealed a clear and critical trade-off between thermal performance and fire safety.
Thermal & Fire Performance Summary
| Criteria | Scenario S1 (EPS) | Scenario S2 (Rockwool) |
|---|---|---|
| Thermal Insulation (U-Value) | 0.573 W/m²K (Better) | 0.638 W/m²K |
| Fire Resistance | Lower (Combustible) | Higher (Non-Combustible) |
| Smoke Emission | Higher | Negligible |
| Structural Integrity in Fire | Moderate | Superior |
1. The Initial Thermal Response
In the first 20 minutes of fire exposure, both walls performed admirably in limiting heat transfer to the safe side. The interior surface temperature increased by only ~3.8 K, well within the safe limits prescribed by NFPA 251 / ASTM E119 / UL 263.
The CFD results confirmed that both assemblies would successfully prevent fire spread via ignition of the unexposed surface during the critical early stages of a fire.
2. The Critical Divergence: Material Behavior in Fire
While the initial heat transfer is similar, the fundamental difference lies in the material’s reaction to the fire itself.
- EPS (S1): As a petroleum-based plastic, EPS is a fuel source. It will melt, combust, and produce copious amounts of toxic smoke, accelerating fire spread and jeopardizing occupant life safety.
- Rockwool (S2): Being a stone-based material, Rockwool is inherently non-combustible. It will not burn, providing stable and reliable insulation throughout the fire event, thereby maintaining compartmentation.
S1: (ESP)
Temperature contours after 1200 seconds:
This chart shows the decrease in Temperature through the three-layer wall after different times (300s,600s,900s,1200s)
- From 0 to 0.15 is the Brick blocks layer
- From 0.15 to 0.2 is the EPS Layer
- From 0.2 to 0.205 is the Mgo sheet layer
S2: (Rockwool)
Temperature contours after 1200 seconds:
From 0 to 0.15 is the Brick blocks layer
From 0.15 to 0.2 is the Rockwool Layer
From 0.2 to 0.205 is the Mgo sheet layer
The Verdict: Data-Driven Recommendations
The choice between EPS and Rockwool is a decision between optimal energy efficiency and uncompromising life safety.
- Choose EPS (S1) if: The application is in a low-fire-risk environment where maximum thermal insulation is the paramount concern, and code compliance for combustibility is not a barrier.
- Choose Rockwool (S2) if: Fire safety and life safety are non-negotiable. For commercial, industrial, and multi-residential buildings, Rockwool’s non-combustible nature provides a critical, reliable layer of defense. It contains fire, limits toxic smoke, and protects structural elements.
For the vast majority of fire-rated assemblies, Rockwool is the unequivocally safer and recommended choice. It provides the necessary balance, ensuring that insulation performance is not achieved at the expense of human life.
Engineer with Confidence! Build with Qomaira!
Material selection is complex, but you don’t have to navigate it based on intuition alone. At Qomaira, we use state-of-the-art CFD simulation and engineering analysis to model your specific designs against real-world hazards. This provides the data you need to make informed, optimal, and safe decisions.
Ready to optimize your next project for both performance and safety?