In teaching the science of the nano world, ball-and-stick molecular models are frequently used as 3D representations of molecules. Unlike a chemical formula, a molecular model allows us to visualise the 3D shape of the molecule and the relative positions of its atoms, the bonds between atoms and why a pair of mirror isomers with the same atoms, bonds and bond angles are two different molecules, etc. These models also show arrangement of atoms in allotropes and molecules forming crystal lattices in materials science. In this article, we describe how to construct molecular models using low-cost toy beads. The retail price of a pack of 36 beads is about 2 British pounds. Such a low cost makes it affordable for most schools to arrange small-group or individual model-building activities. (Contains 17 figures.)