How does Explorer.exe Work?

Hello, recently i have been getting worried of my explorer.exe taking up more memory over time, but is this because it is storing thumbnail catche in case i re-open the folder later? also is there like a preset amount of time before explorer.exe deletes this catche if i don't open the folder in a while, before i rebooted yesterday, my explorer.exe was using about 65,000K of RAM when nothing was running, my computer was not slow but i was worried because it used more memory than everyone i know, when i asked people about their explorer.exe memory usage their was like between 15-20 thousand. right now i am sitting on 41,000 eplorer.exe memory usage, i have a toshiba satellite L505D with 3GB of RAM.