I have some new plastic "Thermos" brand drink ware that says "Dishwasher Safe". If it doesn't Say "Top Rack Only", can I put on the bottom if the top rack is full? I generally wash all plastic up top, but when space is gone, I would like to utilize the bottom.

Any thoughts?

  • 4
    For anybody answering: we already have a question explaining the difference between top and bottom shelf, cooking.stackexchange.com/questions/34414. Please only stick to the "is this item safe on the bottom shelf" part here. You can answer the other question if you want to discuss the theoretical difference.
    – rumtscho
    Dec 27, 2015 at 22:06

1 Answer 1


The reason some products are marked "Top Rack Only", is because many dishwashers have the heating element situated at the bottom of the interior, in close proximity to the bottom rack. It looks and acts much like the heating element in an electric oven.

Typically, this heater comes on during the final rinse cycle, to boost the water temperature. It also comes on during the dry cycle, to "bake" the dishes dry. Items placed on the bottom rack will therefore be exposed to a more intense heat than on the top rack, so things made of plastic can melt or deform.

Your dishwasher likely has options for "temperature boost" and "heated dry". If you turn both off, the heating element will probably not come on. Alternatively, try to place your container in the center of the bottom rack, in such a way that it's as far as possible from the heating element. If you use heated dry, take it out before that cycle begins, and/or check on it during the dry cycle

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