I notice a few builders @ Kalamazoo Expo using foam cores in their bows. What is the main purpose for using this type of material. Thanks for your help and ideas.

Its pretty light for its thickness and its reputed to have sound dampening properties. In a synthetic rig the outer lams (glass or carbon) act like an I-beam. The farther the outher lams are apart the stronger the beam will be. The foam's advantage is that it seperates the outer parts of the "beam" and produces more draw weight with less mass than most core material.

The downside is it tends to  develop micro cracks at the areas where the limb bends the most. Don't know how long the limbs will last.

Bonner

What kind of foam is used?  Is it available to home bowyers and if so from where?

Google syntactic foam. This is not a "foam" that most people associate the word foam with. This will give the information you are looking for.

Old Master Crafters is selling foam lams ~ $35 per pair.

Does OMC have an email address?