What is Passive Purple and How Does it Work?

Passive Purple is the world’s first Passivhaus-certified liquid vapour control, airtight, and smoke tight paint – a high-performance vapour-control membrane that creates a continuous vapour control, airtight, and smoke tight layer across the building envelope. Unlike tapes, foils, or traditional membranes, Passive Purple is spray or roller applied, forming a seamless coating that seals even the most complex details.

Applied to the warm side of insulation, Passive Purple prevents unwanted air leakage through walls, floors, roofs, and junctions. It is suitable for both new builds and retrofit airtightness projects, helping achieve strict UK airtightness standards and Passivhaus performance levels.

Why Liquid Airtight Paint?

Air leakage is one of the biggest causes of heat loss, condensation, and mould in buildings. Different materials such as brick, timber, steel, and concrete expand and contract at different rates, creating micro-cracks in plaster and finishing layers. These cracks become hidden leakage points that compromise airtightness tests and waste energy.

Liquid airtight paint solves this problem. By coating surfaces with Passive Purple, you achieve a flexible, durable airtight layer that adapts to movement in the building fabric, ensuring long-term protection against draughts and damp.

Spray / Roller or Brush Application

• Spray application: Using an airless machine or roller, one installer can apply up to 300m² per day, making it one of the fastest airtightness solutions available.
• Brush application (Passive Purple Brush) - A fibre-reinforced version, ideal for sealing junctions, penetrations, cracks (2-5mm), and smaller projects such as houses and retrofits

Together, the spray and brush systems create a complete airtight solution – from large surface areas to the smallest details.

Suitability of Passive Purple

Passive Purple is suitable for all types of building construction - New builds, Retrofits, Traditional build, Light Gauge Steel (LGS)

The Benefits of Passive Purple

• ✅ Passivhaus certified for guaranteed performance
• ✅ Seamless and flexible – no weak points or overlaps
• ✅ Retrofit ready – apply internally without removing walls
• ✅ Water-based and low VOC, safe for indoor use
• ✅ Works on all substrates – brick, block, timber, concrete, plasterboard, OSB, and steel
• ✅ Permanent airtight layer – can be plastered, rendered, or painted once cured

Airtightness, Explained

• What is airtightness? Controlling unintended air leakage through the building fabric.
• How do you achieve airtightness? By creating a continuous airtight barrier, best achieved with liquid airtight membranes.
• What are the airtightness standards in the UK? New builds must achieve ≤10 m³/h·m² @ 50 Pa, while Passivhaus requires ≤0.6 ACH.
• Why does airtightness matter? It reduces energy loss, improves comfort, prevents condensation, and supports a healthy indoor climate.

Passive Purple and Passivhaus

• What is Passivhaus? A building standard focused on extreme energy efficiency and occupant comfort. Check out the 360 images
• The five principles of Passivhaus: Airtightness, insulation, high-performance glazing, thermal bridge-free design, and ventilation with heat recovery.
• Can it go on Retrofit Projects? Yes it can , check out the case studies
• Examples of Passivhaus projects: Thousands across Europe and the UK now use liquid airtight membranes like Passive Purple to achieve certification.

Preparation & Priming

Great airtightness starts with the right prep. On bare, dusty, porous or lime substrates, prime first with Lime Prime; on dense, sealed or older substrates that need consolidating, use Primer I.M. Once Passive Purple has cured, prime it with Supergrip so plaster and dot-and-dab bond firmly. Right primer, reliable bond.

Quality assurance: Download the free Installation & QA Record sign-off sheet (IM-QA-01) for this product.