The properties and structure of films prepared from solutions of potassium silicate were studied by thermal analysis, IR spectroscopy, and X-ray diffraction. Various SiO2:K2O molar ratios from 2.55 to 4.72 were prepared and studied to determine the effect of molar ratio on the hygroscopic nature, solubility, and intumescence. The results provided insight into the physical structure, and mechanism of water absorption of the potassium silicate films. The molar ratio has a profound effect on the solubility, water absorption, and intumescence of the potassium silicate film. The primary mechanism of water absorption and retention is by ionic hydration. Decrease in the ionic hydration driving force as the molar ratio is increased results in decreasing solubility. Since intumescence results from the release of water vapour, the degree of intumescence decreases as the amount of ionically bonded water decreases with increase in molar ratio.