be VERY CAREFUL about using this stuff. Not that there's any danger from the product itself, but it's capabilities are limited.
last year I bought a bunch of them, and also the other kind that's like a sock filled with gravel. I put all of them into a closet, and closed the door, thinking it would be more than adequate to keep a little closet dry for a while.
When I returned, everything in the closet was covered in mold and mildew. Had to throw a bunch of stuff out, clothes, linens, etc. etc., and used a couple of bottles of cloro cleaning up the hard surfaces. I had been using these things on my boat for years, and they worked great. I figured the humidity in the boat on the water would be more than a closet... boy was I wrong.
I now keep all doors blocked open in the apartment when we are not there. This works fine,... just need that constant air movement.