Seeds that require refrigeration (we label them with a pink note) are species that we don’t dry down completely, so their seeds still contain some moisture. Not drying them down completely helps maintain their viability, but it can also make them more prone to molding. Storing them in the fridge helps prevent any mold. Usually, their time out the fridge while in transit isn’t an issue, but you can check the seeds for any mold growth. If you see mold, it can be rinsed off with a 5% bleach solution.