title_body: Does breaching a stovetop milk steamer's double wall destroy it?
upvoted_answer: The double wall on this steamer is not there for insulation. That idea doesn't add up. An exterior wall will heat up before an interior wall if heated on a stovetop and would inhibit transfer of heat to the interior container...
  
  I can think of two possible reasons for the double wall, but I must say, that double wall is an unnecessary added expense on the unit no matter the reason it was included...
  
  1) In a double wall design, the exterior wall will cool down faster than a single wall would, since the exterior wall does not maintain contact with hot water. This means you can safely reuse the steamer sooner. This is kind of silly, though, since you can easily cool a single walled steamer by briefly running it under cold water.
  
  2) A double walled steamer is more structurally durable than a single walled steamer. These units are sometimes built to withstand very significant internal pressure. The double wall could be part of such a design. This is kind of silly itself because steam pressure higher than a single walled unit could support is dangerous...
  
  The exterior wall in any case likely does not play any part in containing steam. To be sure, I'd need to see the inside of the lid. It depends whether the seal is placed on the outside threads or the inner vessel and whether a gasket is used or not.