The A-side and the B side of the Flex are both very sensitive to moisture. Please store in cool dry area... however when it is time to use again it may have gelled the B side because of the cooler storage temperature. Yes, it is still useable. You just need to heat the B side to no more than 150F, using a hot plate or even a very warm pan of water (making sure no moisture droplets are splashed into the resin) until it returns to its liquid state again. Then shake the B side well, allow it to cool and follow the original mixing instructions.