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I need to create a transparent box that can stay warm inside while in cold temperatures, below 0 degrees, for as long as possible. Glass and plastic are transparent but afaik they don't insulate that well. Is there something else that I could use?

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    $\begingroup$ What are your requirements for the temperature difference? What dimensions are required? Is there a specific chemical requirements (e.g. will it dissolve some materials)? Does the whole box need to be transparent? Does it need to be transparent or translucent? $\endgroup$ – hazzey Feb 4 '16 at 13:47
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    $\begingroup$ I voted to close this because it's too broad. You have no specifications on your project, so you could just make a box with extremely thick walls (1m thick glass) to help insulate, or you could use insulated windows as @CarlWitthoft describes, or you could put a heater in it, or you could put it on a heater (it has to sit on something unless it's levitating), or or or. . . without any clearer idea of what your end goal is and what your limitations are (maximum heat loss, weight, definition of transparency, etc.), this is too broad. $\endgroup$ – Chuck Feb 4 '16 at 13:47
  • $\begingroup$ @hazzey: Not sure what you mean by requirements for temperature difference, just as warm as possible for as long as possible, really just looking for the best material. Dimensions are length: 1m, width: 1m, height: 3m. No chemical requirements although non-toxic is preferable. The whole box needs to be transparent so that sunlight can get in. $\endgroup$ – Hooli Feb 4 '16 at 13:55
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To borrow from a certain Brit physician, "I think it's a bit more complicated than that." For example, you could build/buy a double-walled box with a vacuum between the layers. That's esssentially what a thermos bottle is; there are varieties of drinkware that are built this way. But if you were to build a double-walled glass enclosure that's not evacuated (i.e. easier to build), then fluid dynamics comes into play. While dry air is a pretty good insulator, heat transfer depends both on the thickness of the layer and maintaining a static environment. Too thin, and not much insulating power. But, as manufacturers of storm windows know, if the spacing exceeds about a cm or so, the air starts to form a vortex, moving up on the warm side and down on the cold side. This leads to a lot of conductive heat transfer at the glass-air interface.

Unless you really absolutely positively have to make the entire thing transparent, consider leaving a "peep hole" but covering the rest with a reflective metallic surface.

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