architectural membrane association
ETFE is a film made of copolymer extruded into thin films, that has been around since over 30 years. Firstly used in the naval industry it began to make its way into the textile architecture due to its high transparency and lightweight. Weighting around 1% of glass, it constitutes a great alternative to glazed building envelopes, reducing the mounting system needed to support the foils. It is mostly used for the design of pneumatic shapes like cushions (two to four layers) but can also be used as a cable supported single layer system.
The ETFE foil is unmixed which means that it is 100% recyclable. Due to its lightweight property, the materials needed for support are much less than in a glazed system, bringing the embodied energy (the sum of all the energy required to produce any goods or services) to less than half of that of a glazed system.
ETFE has a life expectancy of over 35 years, with zero to no change of its properties: colour, translucency and transparency. It has a transparency of 90-95% of the total light spectrum and 83-88% of the ultraviolet light, which means it is perfect for cooler weathers. Its weight is less than 1% of glass, allowing the designer to cover vast areas using less secondary structure and foundations.
Manufacturing and Installation
For the manufacturing of ETFE-Foil structures not only proper tools are needed but also good trained and schooled specialists. The layers of ETFE-foil are welded by using a heat bar which, under a certain pressure within a given timeframe, plasticizes them. This is followed directly by using a cooling bar under pressure which “freezes” the seam in its new configuration. This process can also be done using a continuous welding machine. During the manufacturing process (and also later) the manufacturer has to assure a soft handling of the foil to avoid sharp knits, fingerprints and dirt/dust in the interior part of the cushion.
The ready-made foil cushions will then be fixed into a special aluminum profile which more or less works like the frame of a window. After pre-installation, a compressor will be adapted to stabilize the cushion. The air pressure used will be defined by an statics analysis.
Cleaning and Maintenance
ETFE Membranes are self-cleaning, the outer layers are cleaned by the rain and the inner layers repel dirt due to its low friction coefficient. Inspections are recommended though, primarily to locate possible damages caused by mechanical impacts which, if already existing, can in most cases be repaired directly on site.
In a lightweight structure the cost of a foil may range between 5 and 50% of the project total cost. The product itself is allocated in the high cost range for such foils, however the real influence may derive from handling and installation tasks more than the product itself.
ETFE is flame retardant, however very comparable in many international normative as low-flammable. The foils behaviour in fire case is however very resistant to heat and flames and does not promote the spread of flames because it self-extinguishes and does not generate any flaming droplets or particles. There are different types of ETFE that can be found in the market:
Entirely free from toxic heavy metals (e.g. lead and cadmium), halogens and other toxic elements. Since it is an unmixed material, it is 100% recyclable. Due to its lightweight property, the materials needed for support are much less than in a glazed system, bringing the embodied energy (the sum of all the energy required to produce any goods or services) to less than half of a that of a glazed system. It has a very low carbon foot print, the material itself and the projects using it.
ETFE has zero risk of breakage, giving the architect no constructive limits when used as an overhead glazing. To control the thermal properties, several strategies can be used:
ETFE is mostly used for exterior building. Two or more sheets of ETFE foil are usually assembled into cushions, joined at the edges to form the cladding and then inflated by a compressor (whose consumption can be compared to that of a vacuum cleaner). These structures are very popular for sport building applications like football stadiums, as well as courtyards, shopping malls, atria and stores