Why are some items only ‘top rack dishwasher safe’?



What is the difference between the top and bottom rack?

In: Other

The proximity to the giant heating element at the bottom of the dishwasher.

When the dishwasher goes into its dry cycle, that heating element gets really really hot, the top rack doesn’t get nearly as hot as the bottom rack.

Picture sitting right next a fire place versus across the room on the couch. Sure the fireplace warms the whole room, but sitting on the hearth is WAY hotter.

So if you’re made out of plastic that could warp or deform from high heat, you should stay on the top rack.

The top rack water has a slightly lower temperature – so some things (like plastic items) are less likely to melt/warp

Most dishwashers have a heating element under the bottom rack for heating the water and drying; top rack items can be damaged (melted/warped) by the extra heat.

The heating element for drying is at the bottom of the dishwasher, and due to its proximity can melt plastics.

Modern higher cost dishwashers place the heating element in the water pump and super-heat the water (which also sanitizes) during final rinse so that moisture will dissipate. Meltable dishes are safe top or bottom.

A lot of plastics used in food containers are from the polyolefin family of polymers, polyethylene (HDPE) and polypropylene (PP), which get soft and begin to deform at 140F and 180F, respectively. The heating element in many dishwashers is at the bottom, so it’s more likely that deformation of those plastics will occur the closer they are to it.

Most plastic containers are made from these plastics because they A) are food safe (aka generally unreactive to the compounds found in food and do not leech chemicals or break down when exposed to food) and B) are cheap as hell.

For example the clear parts of Rubbermaid containers are usually HDPE and the lids are usually PP. Nalgene bottles are usually some specialized form of HDPE.

Bottom rack gets too hot. Some items can melt if it’s too hot but not melt if it warm. Hence those items can go in top rack and not bottom rack.

Can I use this thread to ask why my dishes are left with water/soap spots after my dishwasher is finished?
Is it the detergent I’m using?

There is a difference where you put your dishes in the diswasher? Had no idea