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Q & A: What is the best insulator?

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Most recent answer: 08/24/2020
Q:
what is the best insulator to create a thermos???
- supre (age 21)
NewYork america america
A:

The best insulator in the world right now is most probably aerogel, with silica aerogels having thermal conductivities of less than 0.03 W/m*K in atmosphere. of aerogel preventing ice from melting on a hot plate at 80 degrees Celsius!

Aerogel has its amazing properties because it's mostly made out of air. In the manufacturing process, first you create a gel, then you remove all the liquid in such a way that the gel walls don't collapse, thus leaving tons of little air pockets. These air pockets then basically shut down conduction and convection, making heat transfer very slow. The way they remove the liquid is really cool - it doesn't work to just evaporate it, because that would end up collapsing the gel, so they actually need to heat up the liquid past the liquid-gas critical point to become a supercritical fluid, then maneuver it back down to a gas. It's nuts!

I think a thermos with an aerogel core is a very good idea. In fact, they already exist, and you can find some for sale online!

Matt Z.

Another material that's often used in good lab thermos bottles, called cryostats, is vacuum with layers of superinsulation wrapping. The wrapping is thin plastic (Mylar) coated with a film of aluminum. The vacuum means that there are very few air molecules to conduct heat, and the mylar keeps them from traveling far, sort of like the aerogel. The aluminum reflects thermal radiation, keeping it from carrying heat well. Mike W.


(published on 02/08/2015)

Follow-Up #1: foam insulators

Q:
Hi. There are many commercial insulators (polyurethane foams) that are much better than aerogels. Aerogels cannot have a thermal conductivity less than that of air - but closed-cell polyurethane foams (and similar) can have alternative gases in the 'bubbles'. I have measured K = 0.020 W/ m K in a shop bought product and I have seen 0.018 W /m K claimed. Obviously the foams don't work at ultra high temperatures but they are still better than aerogels and air.Measuring these low thermal conductivities is actually a great lab experiment if you are interested. https://protonsforbreakfast.wordpress.com/2020/08/24/measuring-the-thermal-conductivity-of-insulation/Best wishesMichael de Podesta
- Michael (age 60)
London, England
A:

Thanks for this info.

You're right that the way aerogels are made requires an open structure through which gases can diffuse. Ordinarily that would mean that after exposure to air the internal gas would be air, which conducts heat more than higher molecular weight gases. That's a fixble problem, however. A different gas could be diffused in and then the surface of the aerogel could be sealed with a lacquer.

Mike W.


(published on 08/24/2020)

Follow-Up #2: insulating boxes

Q:
Hello, we manufacture Gel Packs for keeping food cool during transit - how would you apply your theory to an insulted liner to fit into a box? - I would be very interested. thanks
- Chris Birch (age 49)
Derby (UK)
A:

I think that aerogels are a bit on the delicate side for such applications. Perhaps ordinary polystyren is most practical. An aluminized mylar wrap around it would help reduce thermal  radiation heat input.

Mike W.


(published on 06/12/2020)

Follow-up on this answer.