EPS vs Mineral wool

When planning an External Wall Insulation (EWI) project, one of the most important decisions is the choice of insulation material. The two most common options in the UK are Expanded Polystyrene (EPS) and Mineral Wool. Both materials are widely used, proven in performance, and fully compatible with modern render and cladding systems. However, they differ in thermal properties, fire performance, cost, and application.

This page provides a clear comparison of EPS and Mineral Wool, helping homeowners, contractors, and architects choose the right solution for their project.

What Is EPS?

Expanded Polystyrene (EPS) is a lightweight, rigid insulation board made from expanded beads of polystyrene. It is one of the most cost‑effective insulation materials available and has been used in EWI systems for decades. EPS is easy to cut, shape, and install, making it a popular choice for both new builds and retrofit projects.

Key characteristics of EPS:

• Excellent thermal performance with low thermal conductivity.

• Lightweight and easy to handle on site.

• Cost‑effective compared to other insulation types.

• Resistant to moisture absorption.

• Long service life when properly installed.

What Is Mineral Wool?

Mineral Wool (also known as Rock Wool or Stone Wool) is a dense, fibrous insulation material manufactured from volcanic rock. It is highly regarded for its fire resistance, acoustic performance, and breathability. Mineral Wool is heavier than EPS and requires more careful handling during installation, but it offers superior performance in certain areas.

Key characteristics of Mineral Wool:

• Non‑combustible and fire‑resistant up to very high temperatures.

• Highly breathable, reducing the risk of trapped moisture.

• Excellent acoustic insulation, reducing external noise.

• Strong thermal performance, though slightly lower than EPS.

• Heavier and more expensive than EPS.

EPS vs Mineral Wool – The Key Differences

• Thermal performance: EPS generally provides slightly better thermal conductivity, meaning thinner boards can achieve the same U‑value.

• Fire safety: Mineral Wool is non‑combustible and offers superior fire resistance, making it the preferred choice for high‑rise and public buildings.

• Moisture and breathability: Mineral Wool allows walls to breathe, reducing condensation risk. EPS is more resistant to water absorption but less breathable.

• Acoustic insulation: Mineral Wool outperforms EPS in reducing external noise.

• Cost: EPS is significantly cheaper, making it attractive for budget‑sensitive projects.

• Weight and handling: EPS is lightweight and easy to cut, while Mineral Wool is heavier and requires more careful installation.

• Durability: Both materials are long‑lasting when installed correctly, with lifespans of 25–30 years or more.

Which Should You Choose?

The choice between EPS and Mineral Wool depends on project priorities:

• Choose EPS if: budget is the main concern, maximum thermal efficiency is required, and the project is a low‑rise residential property.

• Choose Mineral Wool if: fire safety, breathability, or acoustic performance are top priorities, or if the project involves high‑rise or public buildings where regulations demand non‑combustible insulation.

Applications in the UK

• EPS: widely used in residential retrofits, new builds, and projects where cost and thermal efficiency are the main drivers.

• Mineral Wool: preferred in urban developments, high‑rise buildings, schools, hospitals, and any project where fire safety and acoustic comfort are critical.

Frequently Asked Questions

Is EPS safe to use?
Yes. EPS is safe when used in certified EWI systems, but it is combustible, so it is not recommended for high‑rise applications.

Does Mineral Wool cost more?
Yes. Mineral Wool is typically more expensive than EPS, but it offers superior fire and acoustic performance.

Which material lasts longer?
Both EPS and Mineral Wool can last 25–30 years or more when installed correctly.

Can both be used with silicone render?
Yes. Both EPS and Mineral Wool are compatible with silicone and acrylic render systems.

Conclusion

EPS and Mineral Wool are both proven insulation materials for external wall insulation systems. EPS offers excellent thermal performance at a lower cost, making it ideal for residential projects where budget is key. Mineral Wool provides unmatched fire resistance, breathability, and acoustic performance, making it the safer choice for high‑rise and public buildings.

By understanding the strengths of each material, property owners and contractors can make informed decisions that balance cost, performance, and compliance.

👉 Ready to discuss which insulation is right for your project? Contact us today for expert advice and tailored recommendations.