foam on speaker?

Just mooching around the forum and noticed pictures of speakers for diy subs, why is the foam (which looks as if it is for sealing the speaker) on top of the fixing plate?,all of the diy subs show the speaker sitting on top of the baffle.so the foam is redundant.
Can i use the wavy carpet rubber underlay to line the sides of a sub i have nearly finished?or is there no alternative to egg crate foam.

 

loft insulate is ideal for subs and is cheap and works well

 

The gaskett on the front is there for those people who want to fix their driver in 'backwards' for maybe making an isobaric sub etc.

 

Thanks Retro and trevor.
Trevor is'nt loft insulate used to fill a sub not line the walls of a ported sub (which mine is and did'nt mention above)and would the fibres not be ejected through the ports?.
ReTro i have seen you linked to a lot of diy subs what do you use to line the inside of the panels?Is it essential as on another forum somone told me they never line ported subs as it is not needed.

 

I use Dacron for filling and got lining a grey foam egg crate stuuf from CPC. It's pretty cheap stuff but seems to do the job.

 

thanks