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I've let the frozen handwarmer sit on my desk for hours, and it's now at room temperature, but still crystallized. So, OK, these things seem to self-activate when they're cold enough. I'm not sure if it's chemically based, or physically based. It could be that eventually the activator disc flexes or is flexed. The crystals seem to radiate from the disc, so it's not purely spontaneous. Anyway, more science needs to be piled on this topic before I can build and answer.
2009.12.04 at 2:00pm EST
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