Now that the Space Shuttle is being decommissioned, what are we to do with all that lovely high-performance insulation that protects it from the heat of re-entry?
Silica aerogel is an amazing material: a solid foam consisting of over 95 per cent air, about the least material and the most 'hole' per unit volume and thus the lowest bulk density of any known solid. It is made from the most abundant elements on Earth, is non-toxic and doesn't burn. What's not to like?
Aerogel makes for fantastic insulation, providing about twice the resistance to heat per unit thickness compared to the next-best materials, and is used in everything from super-energy-efficient skylights and industrial refineries to keeping warm the electronics at the heat of the Mars Exploration rovers. (OK, the Space Shuttle LI-900 insulation tile core is not quite aerogel, but is a very close cousin made of silica glass fibres and 94 per cent air by volume and can withstand temperatures of well over 1000C.)
So how does aerogel manage to outdo every other insulation material by such a margin, and do goats and the environment need to be sacrificed to make it?
With off-the-shelf building insulation such as rigid foam and glass wool loft insulation, the performance is dictated not so much by what the material itself is made of but rather by the (small) holes in it neither available to conduct heat nor convect. Those holes are filled with air or a gas such as pentane.
Silica aerogel basically has more hole than other insulators, and thus conducts less heat through what is left, which is itself is a poor conductor.
The embodied energy of aerogel (ie used in manufacturing it) is less than most alternatives other than wool, and unlike foam, nasties such as toxic "blowing agents" aren't required so leaks/emissions can't happen, and nor can there any ensuing degradation in insulation performance over time. Aerogel insulation should be good for 50 years or more.
One downside of the material is that it costs several times that of other products, but that might well drop if aerogel were suddenly to be made fashionable by Grand Designs or its ilk. Another is that it can be hard to work with (and my builders quietly though unconvincingly vowed never to touch it again: see below).
Aerogel can also be bought in various forms and from many suppliers - Cabot amongst others offers translucent granules and 'privacy' glazing with very good thermal performance (it is also a strong absorber of infrared), diffusing light and preventing anyone seeing straight in; good for skylights and ground-floor windows.
Aerogel was first made in 1931 by Samuel Kistler, in Stockton, California. He went on to invent the silica-based Monsanto Aerogel, which was marketed until the 1960s. It was forgotten until many new scientific and industrial uses were found for it in the Eighties (see History). The blanket style now in my walls has been around for about a decade. And, no, it doesn't seem to taste of anything much.
In the home
I've been working for the last two or three years towards making my family home (and office) "zero-carbon" for electricity and gas. I caught the conservation bug in late 2007 and I was able over a couple of years to reduce electricity consumption at home by about 80 per cent, and then take us negative by putting lots of photovoltaic paneling on the roof.
I also wanted to see what we could do about gas heating.
It was not at all clear how we could insulate the walls of our timber-framed house without giving up too much space, so I concentrated on improving the living room where the family spends much of its time. The decor was a bit of a mess anyway, so we could potentially kill two birds with one stone.