Is XPS insulation Water-Resistant?

Is XPS Insulation water-Resistant?

Is XPS insulation water-Resistant?

Yes, XPS insulation is water-resistant. Its closed-cell structure and hydrophobic nature prevent the infiltration of water and water vapor, making it suitable for various construction applications requiring moisture protection.

XPS Cellular Structure:

XPS insulation Foam is manufactured using a closed-cell structure, where the individual cells are closed off from one another. This structure helps prevent the infiltration of water molecules.

XPS Insulation is Water-Resistant due to Hydrophobic Nature:

XPS is inherently hydrophobic, meaning it repels water due to its composition. The closed-cell structure and the nature of polystyrene make it difficult for water to penetrate.

Moisture Barrier:

XPS Board acts as an effective moisture barrier when properly installed. Its closed-cell structure blocks the movement of liquid water and water vapor, reducing the risk of condensation within walls or roofs.

Water Vapor Resistance:

XPS foam has a low water vapor permeance, which means it inhibits the passage of water vapor. This property is crucial in preventing moisture buildup that can lead to mold growth and structural damage.

Installation Considerations:

While XPS itself is water-resistant, proper installation is essential to maintain its effectiveness. Ensure that the insulation panels are securely attached and joints are tightly sealed with appropriate tape or sealants to prevent any potential water penetration through gaps.

Below-Grade Applications:

XPS is commonly used in below-grade applications, such as insulating foundation walls. Its water-resistant nature helps prevent groundwater infiltration into basements.

Roof Insulation:

XPS is also suitable for roofing applications. Its ability to resist moisture helps protect the roofing system from water damage and maintain its insulation performance over time.

Exterior Insulation:

XPS insulation can be used in exterior insulation systems. Its water-resistant properties ensure that rain and other external moisture sources do not compromise the insulation’s efficiency.

Siding Compatibility:

When using XPS beneath siding materials, ensure proper drainage and ventilation to prevent any potential moisture buildup between the insulation and the siding.


While XPS is resistant to water, it’s important to periodically inspect the installation for any damage or shifts that might compromise its water-resisting capabilities.

Other Waterproofing Measures:

For areas prone to high moisture, combining XPS with additional waterproofing measures like drainage systems and proper grading can provide comprehensive protection against water intrusion.

In summary, XPS insulation is inherently water-resistant due to its closed-cell structure and hydrophobic nature. Its ability to prevent the infiltration of liquid water and water vapor makes it a reliable choice for various construction applications. To maximize its waterproofing effectiveness, proper installation and integration with other building systems are crucial. Always follow manufacturer recommendations and local building codes for the best results.


  1. James on 06/09/2023 at 9:48 AM

    Is XPS insulation suitable for my basement?

  2. Daniel on 06/09/2023 at 9:50 AM

    How do I maximize XPS insulation’s water resistance?

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