EPS Core stands for Expanded PolyStyrene. This core is stiff, light & water resistant. EPS is made using small expandable beads that inflate with heat.
These are expanded in a mould which has a smooth finish. The expanded beads trap air between the polysterene which gives it's lightweight property.
This is the choice of core's for beginner boogie boards as the core is molded with rails & channels & only require the deck, rails & slick skin to be heat laminated to finish. This keeps the manufacturing cost down.
EPS is very brittle & the cells come apart under pressure, so the core can easily snap when bent to far. The smooth core finish does not bond well to the deck & slick, so can easily delaminate. The core also releases trapped air when exposed to heat which can cause bubbling under the deck & skin when exposed to sun or hot area's such as car's etc.
This is a great choice for a kids first bodyoard but not recomended for longevity.