The foam core is the heart of your skimboard. It must be strong and very lightweight. Syndrome originally used Poly Vinyl Chloride (PVC) foam as a core material - pretty much the industry standard for high performance skimboards. It's strong, lightweight, and has proven itself as a core material for over 50 years. But PVC foam is older technology, so research and development in newer, more modern cores led Syndrome to a foam that has proven itself in the offshore racing market as a dependable, durable foam that can withstand high impact forces. In 2004, Syndrome began fabrication with SAN foam. Styrene Acrylo-Nitrile (SAN) foam has very similar strength properties to PVC foam, and one characteristic that really shines - toughness. PVC foam is brittle and can crack easily when bent too far or impacted abruptly. SAN foam is much tougher and can absorb impacts without cracking or delaminating from the skin laminate. This toughness is what makes SAN foam the perfect performance core for your skimboard. All boards are made with 5/8" thick core foam.