Why can't thermos flasks go in the dishwasher?

[alittleteapot]

or is it an urban myth?

I think the glass ones aren't dishwasher safe and you don't want broken glass in your machine.

the class ones usually are sealed into the container and the sealant would break in a dishwasher.

I don't know - my recently purchased satinless steel Thermos' instructions say not to put in the dishwasher - so I don't do it - but not sure why either. Perhaps the rubber band seals on the lid etc would degrade or perhaps water could get in to the air layer of the main flask somehow?

Ah, thanks. That makes sense. Any idea why my warm milk seems to curdle in flask through the day??

i've put a stainless steel flask in the dishwasher - came out sparkling inside and out no probs whatsoever !