What are Roll bar inserts?

[airboxster]

I saw this mentioned in a post about things to know about a boxster before purchasing.

These are the plastic inserts that are part of the Windstop. They are a black/grey plastic with lots of holes- like a screen. One fits into each side of the roll-bar opening.

Sometimes these get stolen. Or the seller removes them, prior to closing the sale, so he/she can make a few extra bucks by selling them elsewhere.