Product review (5 stars): Well packaged, handy product that performs as indicated!
I purchased these to regulate the moisture level inside my firearms cases. The case I'm using has open-cell foam, which is known to retain moisture, so I wanted to make sure none of my guns would rust while in storage.

The strips came in a sealed package, without which they would be ineffective because they would be exposed to moisture on delivery! I purchased them about a month ago along with some silica packets, placed both of them in the case, and sure enough, given that I live in a medium-humidity foggy environment, the strips have registered a slight increase in relative humidity, as seen in the pictures.

I would recommend these as a cheap way to get a rough idea of humidity changes in a closed container.

I purchased silica packets from this manufacturer and they provided me with a sample of these humidity indicator cards to accompany them, but my review has not been influenced otherwise.