Heated air dryers?

[Katemax82]

I'm probably being stupid but while browsing heated air dryers I'm left wondering why they have covers? Doesn't that trap the moisture in? Or am I missing something?

It traps the warm air in. I don't have a cover on mine, but I accidentally discovered how that worked better when I was trying to dry some sheets too, draped over the top.

Makes the heat be more concentrated in that space to help it dry quicker. There’s vents on side to let moisture out

Cool