Yes, I have been using those moisture indicator cards for decades. When I was manufacturing systems for industrial automation destined for tropical locations, part of our warranty process was that the customer had to perform regular maintenance and ensure that the interior desiccant was replaced periodically. The only way we were able to enforce this was by hiding moisture cards inside the case with a tamper-evident seal.
I have never stored a spool in a vacuum bag without a moisture indicator card. What I like about the moisture indicator cards is that they not only are reversible during the filament drying cycle—just include them along with the desiccant bag when you dry the filament—but unlike hygrometers, which only measure moisture at that instant, moisture cards register moisture accumulation over time. This is a fantastic way of ensuring that one can see if the filament truly needs to be dried. You could make the mistake I made early on by placing a desiccant bag inside a vacuum bag and thinking the job was done because the hygrometer registered low humidity. However, a moisture card tells a more accurate story if dried and stored along with the spool.
Warning: Lots of Counterfeit Moisture Indicator Cards on Amazon
But be warned, though. You have to test these cards each time you buy them. There are a lot of counterfeit cards on Amazon that are simply printed ink and don’t have any functioning indicator.
The best example, in my experience, was the cards that came with the Amolen vacuum bags. I complained to Amolen, and they sent me an entire new kit with a pump and all, but the cards were also defective, indicating that they are just a packager of this product and do zero quality control.
Here is Amolen kit that includes counterfeit cards from a brand called “Excellent Technologies”. Try Googling that term and see what you come up with. Typical Chinese ripoff that selects a fake name too common to find.
https://www.amazon.com/dp/B09G649KS7/
Here are legitimate cards I actually tested and verified. But don’t take it for granted. Test them each time. I simply use a measuring cup with water and steam it in the microwave.
https://www.amazon.com/dp/B09JBQM1DF/
Example of the Amolen cards when left inside a steam bath. Note that the indicator did not change at all. Amolen agreed and that’s why they sent me a replacement of the entire kit. I didn’t bother hitting them up a second time when those too turned out to be counterfeit, I just simply switched vendors.
Aside from doing a steam test, below is how you can tell if the cards are likely counterfeit before even attempting a steam bath.
Note the consistent appearance of the blue across the 10% - 60 % circles.
Counterfeit Indicator Cards
Now contrast with real moisture cards from Wise HC these came right out of the moisture sealed Mylar zip lock bags. Notice that the print black circles are very similar to the counterfeit cards but what you’ll also notice is that the color of the blue is very different in the real cards. I’ve since learned that you can’t get pure blue using indicator ink at the 10% mark. If it’s too consistent across the swatches, it’s likely fake like the “excellent technologies” cards in the Amolen kit.
Real Indicator Cards
The second unscientific test is to look at the back of the card for indicator bleed-through. The counterfeit cards don’t have this, the real cards show a gradual increase in chemical indicator.
Unfortunately, it’s hard to capture the difference in a digital photo but hopefully it will be visible enough in this image.
