system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are some items only ‘top rack dishwasher safe’?

What is the difference between the top and bottom rack?
gpt
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.