Passive Purple X (10kg) - Spray/Roller

What is Passive Purple X and How Does it Work?

Passive Purple X is a fire-rated, airtight, watertight and breathable liquid membrane for new-build projects. It is spray or roller-applied to form one seamless coating, replacing the separate layers and laps of a traditional membrane.

Applied internally or externally, it stops air and rain getting through while allowing water vapour to escape, so the building fabric can dry out. It's available in white, cream, black or purple and shares the tested performance of Passive Purple External.

Why Breathable Airtight Paint?

Trapped moisture can damage the building fabric, so a wall needs to keep out air and rain while still being able to dry. Using separate products for fire, water, air and vapour also creates more interfaces where a detail can fail.

Passive Purple X brings those functions together in one continuous layer. With a vapour resistance of Sd ≈ 0.6 m, it lets moisture escape while the coating sheds rain.

It isn't a vapour control layer. Where your design needs one, use Passive Purple.

Spray / Roller or Brush Application

• Spray application: Using an airless machine, one installer can cover up to 300 m² per day.
• Roller application: Ideal if you don't have a spray machine to hand.
• Brush application (Passive Purple X Brush): A 5kg brush-applied version.

Suitability of Passive Purple X

Passive Purple X is designed primarily for new builds, for internal and external use, and can be applied to:

• Concrete, brick and blockwork
• OSB and engineered timber panels
• Fibre cement boards and plasterboard
• Insulation panels

Working on an existing building? Take a look at Passive Purple Retrofit.

Fire rating: The Euroclass B-s1,d0 classification applies on A1 substrates with a density of at least 653 kg/m³. The designer and building control body should confirm suitability against the building's fire strategy.

The Benefits of Passive Purple X

• ✅ Fire rated: Euroclass B-s1,d0 on qualifying substrates and ASTM E84 Class A
• ✅ Airtight and smoke-tight: One continuous, seamless layer
• ✅ Watertight but breathable: Keeps rain out and lets vapour escape
• ✅ Crack-bridging: Tested at 23°C and -10°C
• ✅ UV-stable: Tensile strength increases after 500 hours of UV exposure
• ✅ Protects concrete: Class C1 CO₂ and carbonation barrier
• ✅ Water-based and low emission: EMICODE EC2 rated

Airtightness and Breathability, Explained

• What is airtightness? Controlling unintended air leakage through the building fabric.
• What does breathable mean? Water vapour can pass through the membrane, while liquid water and air can't.
• What are the airtightness standards? New homes in England must achieve 8 m³/(h·m²) at 50 Pa or better, while Passivhaus requires ≤0.6 ACH.
• Why does it matter? Good airtightness reduces energy loss and improves comfort, while breathability allows the building fabric to dry.

Passive Purple X and Passivhaus

• What is Passivhaus? A building standard focused on extreme energy efficiency and occupant comfort.
• What are the five principles? Airtightness, insulation, high-performance glazing, thermal bridge-free design, and ventilation with heat recovery.
• What is the certification? Passive Purple X does not hold its own certificates. The Passive House Institute component certificate (Class phB) and Kiwa BDA Agrément are issued for Passive Purple External.

Preparation & Application

Great airtightness starts with the right prep:

• Remove salt efflorescence, dust, loose material and standing water. Damp surfaces are fine.
• Make sure the surface is closed, filling holes and joints with a fast-setting cement-based product or polyurethane foam.
• Don't add water or solvents.
• Don't apply below 5°C (air and substrate temperature), in full sunlight or during rain.
• Apply two coats, letting the first dry before applying the second.
• Clean tools with water after use.

How Much Will You Need?

Coverage varies with substrate type, porosity and surface condition. Use a wet film gauge to check thickness during application.

Quality assurance: Download the free Installation & QA Record sign-off sheet (IM-QA-06) for this product.

Connect the Membrane at Windows and Junctions

Plan the adjoining tape detail as well as the coated area. Our airtightness tape guide covers width and substrate selection, while tape versus liquid membrane explains compatible interfaces, preparation and inspection. Use the specified coating-to-tape detail and check continuity before covering.