ARE THESE REUSABLE?
Sorry, I don't know if they are. I purchased several packs of 4 and have not tried to reuse them.
Yes-as long as they don't get wet. I use them in my waterproof case for my digital camera and just switch them out every few vacations.
Yes I have reused the silica packs multiple i times
You can use them until the silica is saturated. I don't believe you can reactivate silica; only charcoal. On the other hand, they are a good value - use them until they lose their effectiveness and discard.