It is a moisture absorbent, like those little bags that your get in electronic products that say" Do no eat" all over them.
Cabelea’s sell them in varying sizes for guys to put in their gun safes to keep moisture out. And they are reusable, when the indicator dot changes from green to pink, you pop it on a cookie sheet in your oven for an hour and your good to go again. They are really cheap too, I think the last one pound ones I bought for in my safe were like $7.00 at the store, a little more if you have to ship.