Our literature states the shelf life of all a majority of our wood glues as one two years. Titebond Liquid Hide Glue includes an expiration date on the bottle, because it can progressively lose its ability to dry hard, and this change is not visually obvious. Titebond Polyurethane Glue has a one-year shelf life in an unopened container, but is useable as long as the glue remains fluid. Polyurethanes, however, are designed to react when exposed to moisture. Sometimes, they begin to cure, and solidify, after the bottle has been opened. Most of our yellow and white glues, including Titebond Original and Titebond II, remain usable beyond two years. Should Titebond Original become thick and stringy, or Titebond II turn into an orange-colored gel, these changes signify that the glue is no longer usable. The minimum shelf life of Titebond III is stated as one two years. When stored appropriately at room temperature, Titebond III is expected to last beyond its stated shelf life. If thickened, shake vigorously by firmly tapping bottle on a hard surface until product is restored to original form.