custom bumper

I just finished a fiberglass mold of my 96 Civic's front bumper. So now I need to know what the best way to add on to it is. Ive heard foam, what kind and where is it sold? I plan on modifying the stock one to look like this http://216.55.128.40/sonnic2/ExtImages/96_civicc1complete.jpg

the top section of that is basically the same as stock, all that needs to be done is change the opening, and add those vents.

This section is probably better to ask that question.....

http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=1266