I was watering the plants in my balcony when I noticed a wasp sitting on a leaf. I started to observe when it moved away from the leaf , had a closer look found that it was a nest with some eggs in it.
On browsing for wasp nests I found that it was actually a paper wasps nest.The nests of most species are suspended from a single, central stalk and have the shape of an upside-down umbrella. Plant and wood fibers are collected by the wasps, mixed with saliva, and chewed to form paper like material that is formed into the thin cells of the nest.
The nests are a nursery where larvae are kept one to each cell.
Hexagonal shapes are supposed to be best space conserving dimension in nature which has no wastage of space and also minimum wastage between two cells while interiors have maximum space for the larvae to grow up.
Some interesting links http://www.wildwanderer.com/journal/?p=185