This delightful set includes six pieces: three squares and three semi-circles, each filled with red, blue and yellow water. The blocks are permanently sealed and the their windows are made of super-tough plexiglass. The block frames are made of solid rubberwood from sustainable growth forests, and are chunky enough to allow for solid grasping. Younger children will enjoy shaking them to see the movement of the coloured water, while older children can experiment with the combination of individual colours to create new colours. The squares measure 10.5 cm (about 4") on each side.