ETFE and PTFE explained
It’s no secret that polymer materials have a huge influence on our designed and built environment. They come in uncountable varieties and each has a specific purpose. Two of the newest are ETFE and PTFE. These upcoming plastics are increasingly interesting for exterior use.
However, they’re often mixed up – as their spelling is – so we’re taking a look at their differences, and what designers can use them for. It’s important to realise that these plastics are categorised as textiles, as they are best understood as tensile fabrics rather than as building materials. Now, this is changing.
We recently featured this translucent bio-dome, using layers of foil for insulation and transparency. In this design, ETFE cushions filled with air expand and contract to allow more or less light through.
ETFE, or ethylene tetrafluoroethylene, consists of carbon, fluorine and hydrogen, has a higher tensile strength than PTFE, though PTFE will stretch before breaking. It is also more heat resistant, melting at 327°C, which is 60°C more than ETFE. PTFE is far harder to burn, as it requires a higher concentration of ambient oxygen.
PTFE, or Polytetrafluoroethylene, is made of long strings of carbon and fluorine atoms. It’s commonly known as Teflon®, a non-stick coating. PTFE has an exceptionally low coefficient of friction, which means it’s ‘non-stick’. This means it’s a great material for components and fabrics that have lots of wear and tear. It is frequently used in insulation materials. The expanded version is known as GoreTex. After stretching, this material remains abrasion-resistant and waterproof, but the tiny pores created by the stretching mean that the material breathes, too.
Lower embodied energy is an advantage of ETFE, and recent developments have seen a cross-linked polymer, XL-ETFE, which is far stronger than the normal kind. The material has seen a lot of use, most famously in the Beijing water-cube for the 2008 Olympics.
A similar principle is applied in a new bus shelter in Aarau (CH). Zurich architects Vehovar & Jauslin Architektur created the canopy for a bus station using the translucence and strength of ETFE to great effect. In particular, the inflated texture is visible in the internal ‘bubbles’ created by the polymer. Steel cables keep the construction under tension, while the roof is inflated by pumping in recirculated air.
Both materials are newcomers to the building industry. The fluorine makes the materials strong, and development has led to huge improvements in textile quality. ETFE is used more often in architecture. It is easier to produce and tough enough for most applications.
Meanwhile, PTFE is gaining in use in highly technical situations, such as cabling and industrial applications. Its ability to stretch, and its heat resistance make it suitable for many more applications. These are sure to follow!