[Alexeneum]

hey, alex here! This is my question: Is there any material that can keep a coke (example) cold for at least 1-2 hours. I mean, keep the same temperature and not get a lot hotter? Me and my friend are trying to make a "sleeve" that fits 50 cl soft drinks and keeping the drink cool for about 2 hours, but we have no idea what material that could be! It would be best if it could be a relatively thin layer (like 2-5 mm) =) 

I would really appreciate answers!

[Stepan]

Assuming you want to keep ice cold liquid at 0C, when ambient temperature is +25C. 2 options.

1. You use good quality vacuum-wall glass thermos.
2. You freeze your liquid and allow it slowly melt. The better insulation, the longer it will melt.

You also can blow air (fan) over the wet sleeve, but it reduces temperature by a 3-10 degrees C only

[vmelkon]

You can buy a peltier element if you want.
They are also called Themo Electric Cooler (TEC).
They usually contain a 100-200 BiTe crystals.
You pass something like 12 to 15 V at 6 A or so and one side becomes cold and the other side hot. The temp difference between hot and cold is like 68 C.
You need to put a good heat sink on the hot side in order to not damage it.
The cold side can go down to -20 C-25 C at room temperature.

Example:
http://www.youtube.com/watch?v=yXA4I-1kbBc

[Enthalpy]

Still interested in January?

One of the best materials, and probably the most practical, would be to add an ice cube in the container together with the coke can.

Then the thermos bottle isn't absolutely necessary (though it would avoid the ice cube). 2cm walls of polystyrene foam would let the ice cube melt within one hour.

A thermos bottle can be produced for cheap, of injected plastic. I'd take a resilient plastic for safety (not glass), like polypropylene, which is also weldable. Inject an inner wall and an outer wall, metallize them, then weld them to one single bottle. Either weld within vacuum, or evacuate after welding, through a small tube of clean not-outgassing material closed by melting.

In both cases, you need a very tight cap, which is the difficult part of the design.

I saw this question on many forums... Probably the result of a market analysis.

[Enthalpy]

Some ice cubes are enclosed in hermetic soft plastic. Reusable, cleaner for this use.

Instead of polystyrene foam, thick felt would insulate about as well. I feel it fits better a gadget-fun function. The skins must be airtight to avoid convection, condensation and frost.

If the skins are hermetic, CO₂ or krypton or even xenon can replace air at the felt. Krypton gains a factor of 3 over air: keep cold longer, or make the felt thinner.

The opening could be a flap closed by a Velcro, with much fluff at the fold. Maybe better: open the side, not the end; a good fluffy length can then overlap, like half a turn, which is pressed tight by the elastic-mounted fastening.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Such insulating bags to keep a bottle cold are available from Lidl for few months, and the fluffy material won.

It's little more than a sleeve, with thick soft artificial fur that makes it sympathetic.