You used to be able to get ones that were blue when dry, white when saturated. Talk to your camera shop, they will sell it. You can dry it out in the microwave.
edit: It's a very good idea to keep lenses in a dry environment so they don't grow mold
Have you noticed any moisture damage? Is the place you're keeping them particularly moist?
I keep mine in a big padded camera bag inside my house. We have no moisture issues so I see no need to spend money. If you have moisture issues where you store your gear than sure, but your bag will degrade before the lenses.
Cold air has less capacity to hold moisture, which could result in condensation. Unsure if those pads will help much with that, since the condensation won't really be airborne.
Are you subscribed to our RSS feed? You can download the latest headlines and summaries from our stories directly
to your computer or smartphone by using a feed reader.