Cavechat.org

used the heat pack method saturday. Opened the pack when I left the house and it was nice and warm by time i got to the cave. Threw it in the camera case and headed in. When I first pulled it out to take pictures, I was able to take photos immediately and the heat pack warmed back up too. no fogging of any kind, it was great! Thanks for the tip!

Not to get too off topic here but having non-oxygen using heat packs around can potentially be much better than the alternative in an emergency situation. I have heard of one rescue (in a very tight space) where the use of oxygen-eating heat packs caused a bad-air situation.