Amateur astronomers often must pack away dew covered equipment in the early hours when humidity is high. Silica gel desiccants are a great way to control humidity and avoid mold and fungus in equipment boxes. However, the moisture they accumulate has to be discharged often, usually by heating.

Commercial cannisters of silica gel are often made of metal or plastic. Plastic canisters or packets can't take heat well and can require a long time in dry conditions to discharge moisture. Metal ones can be placed in an oven, but often require an hour or more to discharge.

I've found a simple, low cost, way to create flexible, durable, quickly renewed desiccant packs, that I like better than the commercial solutions.

Many products ship with small silica gel desiccant packets, but these are usually too small and easily damaged for reuse. My solution is to fill 3x4" cotton drawstring bags with the small silica packets that are packaged with many products. These cotton drawstring bags are easily found on-line, a few dollars for a lifetime supply. Cotton is durable, easily passes moisture, and stands up well to microwave heating. I like the way a loosely filled bag can be formed to fit the space available.

I keep a bag handy to collect small silica gel packets in it until it is full. I don't remove the silica gel from the packets, if these wear and tear the cotton bag will contain the silica gel granules. You can also purchase silica gel granules in bulk. When a bag is full I write "Desiccant Poison" on the bag and double tie the draw string.

The cotton bags are easily microwaved to quickly drive off accumulated moisture. Paper desiccant packets take the heat better, but the synthetic ones are fine, if you keep the microwave time to less than a minute. I usually use several 30" cycles on high to avoid overheating, opening the microwave door between cycles for moisture to escape. After 5 minutes or so I let the bag cool down for a short time for the last of the moisture to escape.