Dry & Dry Premium Humidity Indicator Cards 20 Pack(Reusable) - 10-60% 6 Spot(20 Cards)

I love these things. Use in multiple areas for 3d printing filament monitoring. (I use a lot of Nylon filament) and just tape to the inside (facing out) on storage containers and driers. I can easily see the humidity inside without opening.

They work so well I thought "pink" was the dry state. Found a moisture issue right away. Silica packets and dehumidifiers are now solving some major issues.I have board games and guitars stored in my finished basement. It is still damp in the summer and these have been great at identifying issues quickly.

These strips work well and their color change seems to agree pretty well with a digital hygrometer in the same container. It's also important to emphasize that they will change back to blue if the environment becomes drier (e.g. by adding desiccant).The only complaint have is that in the range of 10-30 % relative humidity, it's hard to see the color change. Rather than turning bright pink, a couple of the dots will turn "lavender". When the humidity is significantly higher, like 40-50%, then the lowest dots become clearly pink.See my photos. The strip sitting out on the table has clearly pink circles. This was a humid day around 50-55% humidity. If you look at the strips sealed in the bags, you can see that the one on the left has clearly blue circles, but the one on the right has a couple that are "lavender". If you didn't have the blue to compare against, it would be hard to see that difference.So, if you need more accurate readings in fairly low humidity, those little digital hygrometers may be a better choice.The Dry & Dry company, by the way, has responsive customer service. I originally ordered a product that claimed to be made by them, but it was not. I contacted them to confirm and got a reply within a day. I will continue to use them for desiccants and related products.

Use these to check at a glance to make sure your dessicant protection is still good..You'll know as these change color in the presence of dampnessThey're NATO quality & cheap

These are great! I have them placed everywhere I have a concern about humidity and they're working great. I've even put them in a warm oven to recharge them back to a strong blue. I'm not sure why I didn't get them sooner.

I have a host of 3D filament spools and like to store them all in dry storage boxes, some are used infrequently and I'll store unopened spools as well. I bought the cheap $2 humidity sensors but they won't register below 20% and can't be used for really dry environments. These moisture indicating strips are cheaper and more accurate. They are really designed for dry storage measurements. The only downside is they are hard to read and it takes some "practice" to translate the lavender color to moisture value. I initially used a lab grade sensor as a reference and added it to some boxes with a strip to help me understand the color shift. I'm used to seeing the mostly blue dots and can pretty easily tell when the desiccant needs to be recharged. These are much better at monitoring dry storage than the cheapo humidity gages and I highly recommend.

color turns back and forth as long as there's moisture level change.

Damn near worthless. The color change is so subtle that it's almost imperceivable to see any change within a 20% change in humidity on this indicator. The digital display has humidity in upper right corner indicating 41% humidity. Do you see any difference in color shades of the dots on the humidity indicator strip? I can barely see a change in the pink shade at 60%, but it's definitely nowhere near blue. The error margin on these humidity indicators is at least 30%, but could be more.