I can't speak for glass specifically, but polymer scientists are well aware of an effect called plasticization. In layman's terms, small molecules are commonly added to polymeric materials (large, very long molecules) to make them more flexible. This happens because the small molecules act locally as a solvent and increase the mobility of the polymer chains.
For glass, they add certain chemicals to accomplish more or less the same effect. The one that I am most aware of is Boron. Boron is added to glass in the form of boron oxide to produce a glass that doesn't change dimensions with changes in temperature. AKA Pyrex.