You will find that hard urethane foam is a better insulator than vacuum in high-differential dewars.  We can maintain paramollecular deuterium-tritium at 2.3 degrees K for months on end in an evacuated urethane shielded bottle.  Orthomolecular DT of course is more sensitive.  These dewars must be constantly refrigerated to maintain optium energy.

I changed my buddy icon because Physicalist pirated my screen name. Atheists have a way of being obnoxious, but that is because they lack a case. My new buddy icon is the planet Uranus. It will stay so until Physicalist learns his place -- under the front porch.
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Anonymous Comment

Rocmike you forgot to mention Atheists.

Professional Engineer

This ok for chemicals, but not a hot drink in a cup.  Glass would be the worst.  The other materials are described in a generic way, so there is no answer.  If the heat transfer rate is determined for each material, the one with the lowest transfer rate would be the best.  Send me the info you have and I will look up the materials. Styrofoam is most likely the insulator that is best, but there are plastics and paper which are fabricated to do better. The shape - surface area at the top of the cup - can be a significant factor.

Bill Compton Thinks this answer is Helpful:

My preference for insulation of extreme high/low temperatures (where we do not have to consider impact or abrasion resistance) is silica aerogel.  Its index of thermal conduction is around 2,300/cm which makes it an unequaled insulator, but it is despicably fragile and must be handled with utmost care, making it impractical for most cryogenic use.



For most purposes we safely default to urethane polymer as it is amply resistant to heat, resists oxidation/reduction reasonably well, and is remarkably robust.  For most applications, it is ample, and far less expensive than silica aerogel.  If we get into nasty situations where we must contain unstable materials like liquid hydrogen in rough circumstances, PTFE seems to work out very well as it is a superb thermal insulator (well over 1,334/cm) and sufficiently durable to survive most nasty things.


As expensive as it is, the most thermally conductive substance I can think of extemporaneously is diamond.  Diamond transfers 93% of the thermal energy applied virtually instantly, and is quite transparent, making it a most useful material in cryogenic laser use.

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