We've discovered one sort of foam after extensive testing with our own children.This was done to make Shappy lighter for kids to be able to move pieces about on their own while also making sure that the thickness of both of our bases, which ensures strength and durability over time.The base and the support are sturdy but still comfortable and let you feel like you're sitting on a cloud. The trapezoid-like triangles can be used as a sturdy backrest but also as forts support. Finally, the through pillows are super comfy and just cushy, perfect for laying your head on them.