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