Ethylene Tetrafluoroethylene, commonly abbreviated as ETFE, is an innovative construction material proposed as a substitute for glass in skylight applications. It is a fluorine-based plastic that offers advantages over the glass in terms of durability, weight, and transparency. ETFE was originally developed by DuPont as a material for use in aeronautics and was designed to comply with the strict requirements common in the field. Despite limited use in the construction industry in Europe, ETFE is gradually gaining popularity in the U.S. due to its superior characteristics and low cost.
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The main advantage of ETFE is its outstanding light transmission. The material’s transparency ranges from 90 to 95% and, unlike glass, does not block UV, which makes it suitable for agricultural purposes. In addition, it allows for solar intensity control through the incorporation of frit patterns on different layers. ETFE is highly durable, with an exceptional tensile strength to breaking point. ETFE also permits sufficient acoustic transmission (up to 70%). Finally, due to a combination of its physical properties, resistance to environmental factors, and building physics capacity, the material is highly sustainable, energy-efficient, and cost-efficient.
Several areas of application of ETFE can be identified. A multi-layered system of ETFE film inflated with low-pressurized air creates a system with excellent thermal properties. The addition of inflation units provides the ETFE cushion system with resistance to wind and snow loads. The non-adhesive surface of the material creates a self-cleaning effect and ensures easy maintenance. Finally, ETFE film is self-extinguishing, ensuring compliance with fire safety standards.
ETFE has been successfully applied in several structural engineering projects. In addition to significantly reducing a structure’s weight, the use of ETFE offers a 30% reduction in energy consumption, 55% saving on light sources and a 20% increase in heating due to solar energy trapping. As can be seen, ETFE’s potential for energy efficiency maximization is unparalleled.
ETFE is a fluoropolymer initially developed for the aerospace industry in the 1940s and eventually adopted for use in greenhouse construction due to its superiority over the glass. In the construction industry, ETFE is used in the form of thin sheets 50 to 300 µm thick. A single sheet may be either single-layered or heat-welded into cushions. Due to its extraordinary durability and flexibility, it is possible to use ETFE cushions of much greater size than those made of glass. Some European projects incorporate ETFE panels 11 by 17 meters in size. In addition to aesthetic advantages, larger panels also offer better insulation capacity and reduce the total weight of the structure.
ETFE structures are reinforced against external loads by using a pump system. An automated pump inflates cushions with air, ensuring a steady pressure of 200 to 600 Pa, sufficient for withstanding the majority of environmental loads such as snowfall and wind. System monitoring is performed by several sensors that measure the cushions’ internal humidity, temperature, and dew point to maintain optimal conditions.
Another important property of ETFE is its flexibility. Traditionally, structural damage to large buildings is prevented by increasing the constructions’ stiffness. ETFE mitigates these risks by absorbing all changes in a building’s geometry due to its ability to elongate by more than 600%. The multi-layered structure of cushions adds to the structure’s overall ductility and provides additional protection from wind gusts. The extraordinary flexibility also contributes to the strain hardening capacity of the material, represented by a bilinear stress-strain curve. Finally, it is worth mentioning that ETFE’s surface is extraordinarily smooth, making it easy to clean and maintain. Planned maintenance is easy and often considered unnecessary since, in most cases, ETFE structures are self-cleaning.
One of the most common applications of ETFE is for roofing. The cushions used for the purpose are extruded or blown from molten ETFE resin and cut into five-meter pieces of foil. The final product is wound in rolls for storage and transportation. After this, cushions are designed using non-linear analysis software. Each piece is made of several layers of ETFE foil with different properties.
The design of each layer is fed into a CNC blade that performs high-precision cuts. The digital format of the analysis makes it possible to account for a variety of complex factors such as isotropic yield characteristics. After this, the layers are welded together under high pressure and temperature, creating a sealed environment. The welded cushions are trimmed and prepared for shipping. Due to its physical properties, ETFE is very cost-effective to transport.
On-site, cushions are installed with the help of aluminum extrusions. The extrusions ensure additional environmental protection and provide backup drainage systems. The resulting compound is fixed to the primary structure and connected to a plenum and inflation system that must be purged to protect the cushions from debris. A fail-safe mechanism is incorporated to prevent malfunction due to power outages.
ETFE begins to yield at a relatively low level of stress compared to other common materials like steel and concrete. However, this property also results in a considerable advantage in terms of the overall flexibility and ductility of the structure. The rigidity of a structure is maintained by pressurizing a membrane, and its flexibility allows it to withstand significant loads.
An ETFE roof is highly resistant to weather deterioration, both in terms of structural damage and self-restoring ability in the case of minor physical damage. It is also worth mentioning that pressurized cushions offer excellent thermal protection and optimize solar shading. As can be seen, ETFE demonstrates significant potential for the Estidama concept in terms of sustainability and environmental friendliness.