When designing an external wall system, best practice in breather membrane specification is, on the surface, very straightforward: it should be tested to confirm breathability to BS5250 standards, a W1 water tightness rating, 5,000 hours of UV resistance and a Euroclass A fire safety rating in keeping with minimum Euroclass classification for other elements such as cladding.

So far, so simple. However, what appears to be clearcut on paper is often more complex. Some breather membranes on the market have been superficially tested to achieve the necessary ratings but are not designed or manufactured to pass another vital test: the test of time. A membrane might attain a W1 or Euroclass A rating with a one-off process in the confines of a laboratory environment, but that will count for little if it cannot withstand exposure to the elements when installed on a building façade.

As the UK supplier of Safe One, the award-winning breather membrane, ITP Ltd discuss facade specification with many architects, contractors, designers and specialist engineers. Those conversations often reveal how a combination of low durability and inadequate testing has the potential to cause problems with the level of protection and fire safety offered over the lifetime of a building.


Safe One is a coated product which gives excellent adhesion between the glass fabric and the top coating. It ensures breathability as well as water resistance to W1. In contrast, other W1/A-rated membranes on the market are laminated products. Glue is used to bond three elements: glass fabric, a thin film and a perforated aluminium layer.

The adhesion between these three elements is extremely low – it can withstand only 1 Newton of force (10 Newtons is the equivalent of pulling with 100 grams). The below photograph shows the ‘delamination’ of a laminated membrane product, with the three layers separated after pulling with only figure force. With that in mind, consider the likelihood of separation or peeling with exposure to wind, rain and temperature variations, particularly during the open construction phase.

Separation will lead to  water ingress as the aluminium top layer is perforated to make it breathable. The thin layer of film, which gives the water resistance, is no longer properly protected and has very limited UV resistance.

The below images show the same product after 10 weeks of installation outdoors, showing the same delamination after exposure to the elements. If a laminated product like this were installed on a permanently open façade, the constant exposure to the elements would severely deteriorate its condition and ability to function.

Delamination will also jeopardise the class A2 fire protection. With the government’s Building Safety Act applying stricter responsibilities and more rigorous oversight, that could present major problems in the long-term.


Corrosion is another factor to consider in the long-term performance of a breather membrane.  If a product has an aluminium layer which is not protected by a lacquer (which appears to be the case with the above product) the aluminium will corrode over time and form a cover of white dust, accelerating the delamination. In contrast, Safe One’s unique, patented composition has a protective coating, with no aluminium, and will not corrode.

Misrepresentations and omissions in testing and data

A product’s Euroclass A classification can be misleading in the context of its lack of durability, but façade designers should also be wary of crucial misrepresentations  and omissions within the original lab testing methodology. Some manufacturers supply test data for their membrane textile, but not for the integrated adhesive materials they supply to fix it to the façade or to make overlaps (e.g. the two tapes on the below photograph). If the latter does not meet the same fire rating, the former’s credentials are fundamentally compromised.

In some cases, the manufacturer refers to a compliant tape in its test data, but supplies a different, untested tape when it delivers the membrane to site. Serge Ferrari, the manufacturer of Safe One, recently tested two integrated self-adhesive strips which one of our competitors supplies with its membrane.  The tests show that the base material meets class A2, but the material with the two adhesive strips falls short of that classification. It is essential to ensure that a breather membrane has been fully tested as a system, encompassing all elements used within the installation, rather than a material tested in isolation or with reference to elements which are not supplied as standard.

The Declaration of Performance (DOP) is another piece of manufacturer data which requires scrutiny. Safe One’s DOP shows the tests results before and after ageing as specified in the harmonised standard BS EN 13859-2. Some competitors supply a DOP without the results after ageing. It’s impossible to make an informed decision about membrane specification without that data, particularly in relation to open-jointed cladding and permanently open facades. The data is also relevant to the open building phase, when the facade and breather membrane are exposed to the elements. For example, any system that is not fully tested for 5,000 hours of UV resistance cannot be relied upon to resist degradation in other areas of performance.

The importance of independent testing cannot be overstated. If a membrane supplier is unable to provide evidence of independent testing from a recognised testing body, it is likely that the tests were carried out in-house and therefore their findings lack credibility. In the case of fire safety testing, there is simply no room for any doubt concerning methodology and veracity. A membrane must be tested as a complete system, but some suppliers claim this without the independent sources to verify the claim.


The design of external walls is subject to increasing scrutiny. Substandard façade solutions are likely to fall foul of the stricter regulations and more robust oversight of Building Safety Act. Dame Judith Hackitt, who led the post-Grenfell review of building safety, has been critical of progress within the construction sector, frequently asserting that the industry should not wait for legislation to raise the bar. There is an urgent need to identify systems which meet best practice in the construction of the building envelope. Failure to do that now could compromise the safety and longevity of a building further down the line.

The overarching function of a breather membrane is the protection of a building’s long-term durability. If the membrane itself is not durable, then this function cannot be sustained in the long term. While some breather membranes on the market ostensibly meet the right testing criteria  – W1, Euroclass A and high breathability – at an economy price, they fail the ultimate test in practice, undermined by design flaws and inferior manufacturing quality. In contrast, Safe One’s performance and longevity has been exhaustively tested and recognised within the industry, including Product of the Year in the Façade 2022 Design and Engineering Awards.

Unlike rival products, Safe One represents what all good breather membranes should be: a sound investment in the lifetime of a building.


Laminated product prone to delamination/peeling. Coated product with strong adhesion between fabric and coating.
Aluminium layer with no lacquer to protect against corrosion. Protective coating and no aluminium = zero corrosion
Supplied with elements (e.g. adhesive tape) which are not referenced in fire testing. Safe One is tested as system with the glue to make the overlaps included in the A2 tests.
Declaration of Performance does not show tests results after ageing. Declaration of Performance shows tests results before and after ageing.
Not tested as a full system. No industry awards. Independently tested by a recognised body.  Won Product of the Year in CIBSE Façade Design and Engineering Awards.