Passive Purple Is Certified Class A Airtight by the Passive House Institute
When a specification calls for airtightness, "it feels tight" is not good enough. You need a number, and you need it from an independent authority. Passive Purple has both: the Passive House Institute (Passivhaus Institut, Darmstadt) has tested the full Passive Purple system and awarded it the top airtightness classification, Class A (phA). 🔒
What the Passive House Institute actually tested
The Passive House Institute is the body that defines the Passivhaus standard. When it certifies an airtightness product, it does not simply test a flat sheet of membrane in ideal conditions. It tests the system — the membrane and its connections — to DIN EN 12114, the European standard for the air permeability of building components.
The headline result for Passive Purple:
- Air permeability of 0.02 (±0.002) m³/(h·m²), standardised at 50 Pa.
To put that in context, the phA requirement is ≤0.10 m³/(h·m²) at 50 Pa. Passive Purple came in at one fifth of the limit — comfortably inside the very best class the Institute awards.
Understanding the PHI airtightness classes
The Passive House Institute grades airtightness products into classes based on how little air passes through them at a reference pressure of 50 Pa. In descending order of performance:
- phA — the best class, the tightest performance.
- phB — the middle class.
- phC — the entry class.
Passive Purple sits in phA. For a Passivhaus designer, that means it can be specified with confidence as the airtight layer, with a certified figure to hand to the certifier rather than a manufacturer's estimate.
Why testing the connections matters more than the membrane
Here is the part that experienced specifiers care about most. Real buildings do not leak through the middle of a well-applied membrane. They leak at the junctions — where the airtight layer meets a concrete slab, an OSB board, a service penetration, or another sheet of membrane. These are the details that are fiddly to seal with tapes and sheets, and they are exactly where site workmanship tends to fall down.
Because Passive Purple is liquid-applied, it forms a continuous, monolithic layer that carries straight across those junctions. The Passive House Institute tested precisely these connections, and every one of them passed:
- Membrane to concrete: 0.01 m³/(h·m²) @ 50 Pa
- Membrane to membrane: 0.02 m³/(h·m²) @ 50 Pa
- Membrane to OSB: 0.03 m³/(h·m²) @ 50 Pa
Every connection result is inside the phA limit. That is the meaningful proof — not that a lab sample is tight, but that the details a contractor will actually build on site stay tight too.
Independently confirmed at Ghent University
A second, separate body reached the same conclusion. Ghent University tested Passive Purple and Passive Purple External, again to EN 12114, this time sprayed onto concrete blockwork with anchored Rockwool insulation — a real-world build-up rather than an idealised panel.
- Passive Purple achieved 0.019 m³/(h·m²) at 50 Pa, with all configurations reaching ph A.
- Critically, the insulation-fixing anchors that penetrate the membrane added negligible extra air leakage.
That last point deserves emphasis. In many airtight systems, every fixing that punctures the layer is a potential leak that has to be individually sealed. Ghent's testing shows that Passive Purple self-seals around penetrating anchors well enough that they make no meaningful difference to the result.
Why it matters
"Passivhaus certified" is a phrase that gets used loosely across the construction industry. In Passive Purple's case there is a genuine, independent test behind it — from the Passive House Institute itself, confirmed by a second university lab, with a real number you can write into a specification.
For the architect, that means a defensible spec. For the contractor, it means a system that forgives the difficult junction details. For the certifier, it means a documented phA classification rather than a claim. And because Airtight White is the same formulation as Passive Purple, simply white-pigmented, every one of these results applies to it too.
You can read the full test reports and classification documents on our full test data & certifications page, and specify the product itself here: Passive Purple. If airtightness is on your drawings, these are the numbers to build it around.