Originally Posted by Mr B
When shopping silica-gel, get the color-changing stuff. And remember, it's never "used up" just toss it in a hot dry place for a few hours. Like the sauna when preheating it, or the oven after baking. Just over boiling, for a couple of hours. The stuff in the paper bags generally isn't color changing, so just regenerate it before use, just in case.
Another good tip!
IIRC, the colour-changing version is blue when regenerated and turns pink when it's saturated.