Aerogels are synthetic low-density materials formed by removing the liquid from a gel under special drying conditions to create a solid three-dimensional nanoporous structure containing 80-99% air.
Due to their high porosity, aerogels exhibit the lowest thermal conductivity of any solid, whilst being transparent to light and solar radiation. They can be made from practically any material, although the most common form is silica aerogel.
Commercial products for the building sector include:
- Cavity insulation
- Glazing units and cladding systems containing granular aerogel
- Translucent and opaque insulation boards, blankets and tensile roof membranes embedded with aerogel particles
Transparent monolithic silica aerogel has been cited as a future glazing technology, with the potential to achieve U-values as low as 0.1 W/m²K.
ETFE (ethylene tetrafluoroethylene) is a Teflon®-coated fluoropolymer material blown or extruded to form large, durable sheets. Resistant to degradation by ultraviolet (UV) light and atmospheric pollution, it can be manufactured as single-ply sheets or double- or triple-ply air-filled ‘pillows.’
ETFE has very poor thermal and acoustic performance as a single-ply sheet. However, in the double- and triple-ply configurations, it has excellent thermal properties because the air trapped between the layers acts as an insulator. The air-filled pillows are maintained at constant air pressures relative to wind loads by pumps, letting the skin adjust in response to the varying loads. A secondary structure, usually consisting of aluminium extrusions, steel rods, or steel cables is needed to support the pillows.
While ETFE is low-maintenance, recyclable, and, when compared to glass, extremely lightweight, it is also combustible. However, it is inherently low inflammability because of the presence of fluorine in its chemical composition. This makes the ETFE material self-extinguishing. Because it is normally in tension, ETFE softens and ultimately fails at temperatures above 200 °C.
Vacuum-insulated panels (VIPs)
Another emerging yet costly solution to insulation is vacuum-insulated panels (VIPs). Consist of a core of insulation material (usually silica or glass fibre) enclosed in an airtight, VIPs have up to one-seventh the thermal conductivity of conventional insulation materials.
VIPs are not finished materials, so they are used within non-glazed building envelope elements or behind curtain wall spandrels. Because VIPs have such good insulating qualities, their use can decrease the thickness of the building envelope without impacting its thermal performance.
Phase-change materials (PCMs)
Either organic (i.e., waxes) or inorganic (i.e., salts) in their based material, phase-change materials (PCMs) are solid at room temperatures, but liquefy at higher temperatures, absorbing and storing heat in the process. When incorporated into the building envelope, they can absorb high exterior temperatures during the day and dissipate heat to the interior at night.