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I am trying to create a small 10 to 20cm cube that can conserve the heat in 100 to 200ml of 60-90c water in a small Pyrex glass for about an hour. The problem is that I can not use commercial insulators like foam, bubble wrap, and the like. I have searched Google for ideas, but all the results are commercial. I also can not heat or cool the device beforehand, and I have to have a 2cm hole in the top.

I have tried cotton balls and a packed cotton balls with felt mixture, and cotton balls worked the best.

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Shredded up newspaper might work – jonsca Nov 19 '12 at 22:49
This sounds like an assignment (and a cool one) in a class one of my colleagues teaches. – Ben Norris Nov 20 '12 at 2:02 – CHM Nov 20 '12 at 3:48

Often the key with stopping the conduction of heat is to provide as many phase transitions as possible. Most thermal insulators achieve this by having voids of Air which is achieved in a variety of ways, bubble wrap, fibre glass etc.

For a "non comercial" I assume they mean stuff you have lying around the lab?

To attempt this I'd layer blue roll / cotton wool / glass wool with tin foil. The more layers the better.

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Take a carton box in which the glass fits easily. Wrap the outside of the glass with a thin layer of plastic (sandwich bag). Now, buy some gap filler (PU spray foam, aerosol) to fill the rest of the space. The PU foam has good filling and isolation properties. Once it is cured (24h), you can take out the glass and use it when necessary.

Please read the safely instructions on the label !! Good luck.

PS: the justification for buying the PU foam, lies in the that you already spent some time trying to reach your goal.

EDIT: background info:

It concerns polyurethane chemistry. Here in Europe this type of canistered foam is widely used on the building site. Its purpose is predominantly to fill cavities and act as an isolation material. It's made out of an isocyante (R-NCO) and a polyol (R-(OH)n) forming a urethane bond (R-C=O-O-N-H-R). Together with a propellant (hydrocarbons), it is pressed out of a canister. The left-over isocyantes will react with ambient water, to form poly-urea bonds. This embodies the curing mechanism.

The reason for me to suggest this particular product is because it fills easily and shapes any form. It will cure within a couple of hour. Quit often this material is chosen to prepare surprises (packages with surprises in them....)

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