XPS insulation, or extruded polystyrene, has established itself as one of the most effective materials for improving energy efficiency in buildings and civil works. Thanks to its excellent insulating capacity, high resistance to moisture, and durability, this material is increasingly used in projects that prioritize sustainability and thermal comfort. To improve your knowledge on this topic, you can read this article on thermal insulation for the home.
In this article, we explore in depth its technical characteristics, manufacturing process, most common uses, regulatory certifications, advantages over other insulators, and many other key considerations. If you're looking for a material that combines thermal performance with structural strength and long life, XPS may be the ideal solution for your project.
What is XPS insulation?
Extruded polystyrene, also known as XPS, is a type of rigid foam with a closed-cell structure made from polystyrene resins through an extrusion process. This cellular configuration gives it its most notable properties: exceptional thermal insulation capacity, very low water absorption, and high mechanical resistance.
This is a thermoplastic product with ideal characteristics for demanding applications, from facade roofs and skirting boards to buried floors and walls. Its lightness also makes it easy to handle and install, reducing labor time and costs. To learn more about the benefits of different materials, you can check out our guide on Applications of extruded polystyrene in construction.
Technical properties of XPS
XPS stands out for a combination of physical and technical properties that make it one of the most reliable materials in thermal insulation:
Thermal conductivity
The thermal conductivity of XPS is between 0.029 and 0.036 W/m·K, depending on the foaming gas used during its manufacture. This low conductivity allows for high thermal resistance to be achieved with reduced thicknesses. The thermal resistance (RD) is calculated by applying the formula: RD = d / λ, where d is the product thickness and λ its thermal conductivity coefficient. For a more detailed comparison, see our article on comparison of insulators.
compressive strength
XPS offers a standard compressive strength of 300 kPa with reinforced options reaching up to 700 kPa. This makes it ideal for supporting heavy loads on pavements, walkable roofs or areas with regular traffic.
Water absorption
Thanks to its fully closed cellular structure, XPS has a total immersion water absorption of less than 0,7%. Even under more aggressive conditions, such as moisture diffusion in inverted roofs, absorption does not exceed 3%. If you'd like to learn more about how other materials interact with moisture, we recommend reviewing our articles on fire resistance of rock wool.
Dimensional stability and deformation
After being exposed for 48 hours at 70°C and 90% humidity, the changes in dimension of the XPS do not exceed 5%. Furthermore, when subjected to constant compression and temperature, its deformation remains below 5% even after 168 hours.
Perpendicular traction
XPS withstands a tensile force perpendicular to its faces exceeding 200 kPa, providing additional structural security.
Reaction to fire
Classified as Euroclass E, it is a self-extinguishing product that does not generate flammable droplets or spread flames, although it is not the most recommended for areas with high fire-resistant requirements.
Freezing and thawing
After 300 freeze-thaw cycles, its strength loss is less than 10% and its water absorption is less than 1%, demonstrating its great durability even in extreme weather conditions.
Water vapor resistance
XPS has a water vapor diffusion resistance factor (µ) greater than 150, behaving as a highly effective barrier against environmental humidity.
XPS manufacturing process
XPS is manufactured by extrusion, a process that guarantees a homogeneous internal structure and constant properties throughout the panel. The main phases are described below:
- Extrusion: The polystyrene pellets are introduced into an extruder where they are melted together with additives.
- Expansion: A controlled foaming gas is injected that forms the closed cellular structure of the product.
- Cooling and stabilization: The material is allowed to cool and rest to acquire its final shape and dimensions.
- machining: The panels are cut and the edges are profiled to facilitate assembly and minimize thermal bridges.
XPS applications in construction
XPS finds multiple applications in both new construction and energy renovation, adapting to different construction needs.
Flat and pitched roofs
Its high thermal and compression resistance make it the star material for insulating both flat and pitched roofs. On inverted flat roofs, it is placed over the waterproofing, acting as an additional protective barrier. For a deeper dive into the topic of sustainable construction, see our article on bioclimatic houses and thermal insulation.
Facades and perimeter walls
In ventilated facades and exterior walls, XPS is easily integrated into SATE systems, improving thermal performance without affecting the usable interior space. In addition, it protects against moisture and improves interior comfort.
Underfloor heating and flooring
Due to its rigidity and dimensional stability, XPS is an excellent support under radiant floors and flooring in general, preventing downward heat loss and ensuring even heat distribution.
Foundations and buried walls
XPS maintains its insulating properties in humid environments and under pressure, making it ideal for insulating foundations, basements, or walls in contact with the ground. This makes it an essential material in modern construction.
SATE systems with XPS: insulation from the outside
The exterior thermal insulation system (ETICS) with XPS panels offers a complete solution for reducing the building's energy demand. It consists of adhering XPS panels to the existing façade and covering them with mortar and decorative finishes.
This system prevents thermal bridges, condensation, and internal thermal movement, in addition to improving aesthetics and increasing property value. To learn more about maintaining these systems, visit our article on maintenance in aerothermal systems.
Available thicknesses and their recommended use
XPS is sold in multiple thicknesses to adapt to the insulation requirements of each construction area.
- 1 cm: Ideal for light renovations or interiors where space is limited.
- 2 cm: A balanced option between thermal efficiency and ease of installation, recommended for walls, ceilings or floors.
- 3cm or more: Used outdoors, on roofs, and in areas with extreme climates that require high thermal insulation.
XPS Certifications and Regulations
The XPS must comply with European product regulations such as UNE-EN 13164 and UNE-EN 13172, which establish the technical requirements and evaluation procedures.
In addition, manufacturers can opt for voluntary certifications such as the AENOR N Mark, which guarantees consistent quality and compliance with regulatory specifications. It is also important CE marking, mandatory for products marketed in the European Union, which verifies compliance with community directives.
Compliance with European Regulation 893/2006, which regulates the properties of insulation materials, is also essential.
Sustainability and recyclability
XPS is an energy-efficient option and, in many cases, is made from up to 100% recycled materials. This makes it a product aligned with sustainable construction.
Its durability prevents frequent replacements, and its recyclability contributes to a circular economy. In addition, by reducing the energy demand of buildings, it reduces greenhouse gas emissions; to learn more, we invite you to read about ecological insulating materials.
Comparison with other insulating materials
XPS faces various competitors such as glass wool, EPS or polyurethane foam, each with its own advantages and disadvantages.
- EPS: More economical but with lower mechanical resistance and greater water absorption.
- Glass wool: Good sound insulation and fire resistance, but less durable and more vulnerable to moisture.
- Polyurethane: Excellent thermal insulation, but more expensive and with greater environmental impact if not recycled.
XPS stands out as the best in compressive strength, water absorption and maintenance-free longevity, making it a favorite in critical applications.
Installing the XPS: Key Steps
Correct installation is essential to fully exploit the properties of the XPS:
- Surface Preparation: Cleaning and repairing the base to ensure good adhesion.
- Application of adhesives and fixings: Secure the panel to the support with adhesive mortar and plastic plugs.
- Homogeneous placement: Align the panels and overlap the joints to avoid thermal bridges.
- Sealed: Use specific putties to prevent water or air leaks.
- Top coat: Decorative coatings or waterproof sheets as needed.
Maintenance and useful life
XPS is a low maintenance, long life material. Periodic inspections are sufficient to ensure that the insulation remains intact and well sealed.
It is not affected by microorganisms, chemical agents, or insects, which helps preserve its properties for decades without the need for intervention. For more information on the maintenance of other insulators, check out our article on Buying guide for quality insulation.
Extruded polystyrene is established as one of the most robust and durable options for thermal insulation thanks to its versatility, performance, and durability. Its ability to adapt to various structural environments allows it to be applied in both new construction and renovations. With proper installation, quality certifications, and an increasingly reduced environmental impact, XPS is today a safe bet for improving the energy efficiency of any building.
