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Phase-Changing Wax and the One Liter House
Jamais Cascio, 24 Mar 05

German chemical company BASF has developed a new form of building insulation, and is testing it in a complex of employee houses. The insulation, along with high-efficiency windows and other energy-saving features, results in the buildings requiring only about one liter of oil per square meter for annual heating -- 5% of the average home requirement in Germany, and well below the nation's new efficiency mandate of 7 liters per square meter. The new form of insulation?


Underneath the wallpaper is an innocuous looking plaster which is designed to ensure that the interior temperature of the house is always comfortable. The secret is millions of tiny wax capsules embedded within the plaster, which regulate the temperature. These microcapsules measure a hundredth of a millimetre or less, and work on the principle of latent heat. In other words, if it gets too hot outside, the wax melts and soaks up the excess heat, keeping it cooler for longer inside. However, if the weather gets too cold, the wax solidifies again and releases the stored heat. According to Dr Patrick Amrhein, head of the research team at BASF which pioneered these phase changing materials, or PCMs, the microcapsules are so effective at climate control that a mere inch of this plaster has the same heat absorption capability as a 10in thick timber-bricked wall.

BASF is marketing the phase-changing materials specifically to "green building" architects, but the researchers also argue that PCMs will be useful in clothing and packaging. PCM wallboard is currently on sale in Italy and Germany, and soon in the UK. I've found nothing yet indicating that the material will be available to American homebuilders.

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Huh, that's pretty interesting. It's very similar to the evaporative cooling principle where the phase change (water to water vapor) absorbs a bunch of heat. I didn't know that something like wax could be tuned to have it's phase change at a specific temperature (like room temperature). Nor that by tuning it you wouldn't destroy the energy advantage of the phase change. One of those ideas that just makes good sense when someone spells it out for you.

Posted by: Ben on 24 Mar 05

Man, that's amazing. I hope it turns out to work as good as it sounds.

Posted by: Joseph Willemssen on 24 Mar 05

They must have many different waxes with different melting points evenly distributed throughout the plaster, or else it would only really work near one given temperature. I suppose this could be tuned to the mean temperature of a buildings local environment to improve performance. That might not make much difference though; here in (Ontario) Canada, for example our mean temperature is just slightly above 0, with a variance of near 30 degrees year round, So for an insulator would not have a worthwhile effect if it only worked in a 5 degree range.
or of course I could be completely wrong about all of that.

Posted by: Russell Wendt on 24 Mar 05

Perhaps I'm just a worry-wart, but the idea of cladding my walls with anything containing wax makes me fear for fire safety.

That being said, if it is tested and is found not to have fire safety problem, using this with those thermasave boards (, I think) would be ideal... thick polystyrene foam clad not just with concrete, but with concrete with microcapsuled wax. the R values would be amazing :-)

Posted by: Adam Brown on 25 Mar 05

I wonder if the plaster mentioned in the article could be applied to existing structures as well as new ones. The article mentions pre-fab wallboard. Existing structures tend to be the less fuel efficient anyway.

Posted by: Erik Ehlert on 28 Mar 05



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