Will un-mixed Mod Podge Resin yellow over time?

Yes, the hardener part of the Mod Podge Resin will yellow over time. The product has a shelf life of one year unopened and 6 months lifespan opened. Remember to always close the lid on the hardener right after each use and store in a dark area. Exposure to air and sunlight will make the hardener yellow faster. Do the same with the Resin part as it also has the same life span of the hardener but it will not yellow over time in the bottle.