If all the expanded beads were the same size then perfect packing could be expected. Since there is enough dispersion of sizes we get a situation similar to the bubble bath. After all it is a foam. The final image is a micrograph of cork. Also a light-weight material, but in this case one found in nature.
Cork is so light because it is full of air.
It is formed by long empty channels that run perpendicular to the picture. Again, these channels are densely packed but their different sizes and irregularities make the pattern less obvious. Not quite actually. This leopard-like pattern shows the distribution of lines of a magnetic field when they begin to penetrate a superconducting sample. This is a close-up fotograph of the speakers in my computer.