Savinelli Pipe 'Lid' what's it for?

[lawks]

Hello, I recently bought a Savinelli Pipe with a matching colored acrylic 'lid' with aout 1/2" of foam that goes down into the bowl. I'm curious what is its purpose? Once the cake builds the foam will smash it, so I am not sure if it is to be used after it is smoked or no?
Thanks.

Here's a link for a better idea:
http://www.bing.com/images/search?q...35fc9754ceef23737d016642766ebf65o0&ajaxhist=0

 

[Commander Quan]

You can fill it and take it with you for latter, or save a half smoked bowl.