If you’ve ever worked with electronic components, aerospace assemblies, or any product that requires protection from moisture-related damage, you’re probably familiar with Humidity Indicator Cards (HICs). As a supplier who’s been manufacturing and distributing these small, critical cards for over a decade, I’ve learned that the most common question I get from clients isn’t “What’s a HIC?” It’s “How do I properly document humidity readings from these cards?” Too often, I see teams documenting readings wrong—missed steps, incorrect terminology, even misinterpreted color changes—that lead to rejections, delays, or unnecessary costs. Today, I’m breaking down exactly how to document HIC humidity readings correctly, using real-world lessons from the manufacturing floor and client projects I’ve supported. Humidity Indicator Card
First, let’s ground this in why documentation matters. HICs work by using a cobalt chloride-based (or more recently, non-cobalt) indicator ink that changes color as it absorbs moisture. The cards are calibrated to specific relative humidity (RH) thresholds—common ones are 10%, 20%, 30%, 40%, 50%, and 60% RH—so a color change from, say, blue (low humidity) to pink (high humidity) tells you exactly what threshold the environment has reached. Documentation isn’t just paperwork; it’s a legal and technical record. For medical devices, aerospace parts, or military electronics, regulators like the FDA or ISO 9001 require a verifiable trail that these components were stored in acceptable moisture levels. For manufacturing teams, good documentation catches problems early—like a faulty desiccant or a leaky storage bag—before components get damaged.
I start every client call with this advice: your documentation process has to be tied to the context of where the HIC is used. A HIC in a raw material storage cabinet needs different documentation than one on a sealed microelectronic package waiting for installation. Let’s walk through each step, with examples from a recent client who was building satellite components last year. They were missing critical traceability because they were just taking a photo of the HIC and writing the date on a sticky note—no unique ID, no calibration info, no notes about the environment. We fixed that together, and their audit six months later went through without a single non-conformity.
First step, before you even take a reading: prep the HIC and your documentation tool. This might sound basic, but I’ve seen people grab a HIC that’s already been removed from its protective packaging, or use a notepad from the manufacturing floor that’s been exposed to humidity, leading to inconsistent notes. Every HIC from our facility comes with a unique serial number, a calibration sheet, and a packaging label that lists its calibrated RH thresholds. You need to note that serial number first—this is your link back to when the card was manufactured, its calibration date, and its performance history. For example, HIC serial number HIC-2024-0317-0042 was calibrated on March 15, 2024, has a 20% to 60% RH range, and is for single-use. That’s non-negotiable. If you lose that serial number, you can’t prove the card was calibrated correctly, which invalidates your reading.
Next, the actual reading: how to observe and record the color change. This is where most mistakes happen. First, never hold the HIC directly in sunlight or under harsh fluorescent lights—UV radiation can temporarily alter the indicator ink, making it look like it’s changed when it hasn’t. I recommend using a neutral, indoor light source (like 4000K LED, the same color as most office lighting) held at a 45-degree angle to the card. The card’s legend will show the color for each RH threshold: for a standard 20/30/40/50/60 RH card, leftmost is 20% (blue), next 30% (light blue), 40% (lavender), 50% (pink), 60% (deep pink). Wait 30 seconds after opening the sealed bag the HIC is in, too—if you yank it out and read it immediately, the surface ink might have changed, but the core hasn’t, leading to a false high reading.
When recording the reading, don’t just write “pink” or “blue”—be specific with the threshold. For example, instead of “HIC is pink,” write “HIC SN HIC-2024-0317-0042: 50% RH threshold color change observed (matches legend color 5, date 2024-04-12, time 14:27 UTC).” Also, note the ambient conditions where you’re taking the reading: air temperature, if the HIC was removed from a storage bag, how long it was out. For that satellite client, we added a field for “package seal integrity” because a torn bag would skew readings. Last month, a client with a semiconductor fab had a batch of components rejected because they’d written “RH >50%” instead of noting the exact threshold, and the auditor couldn’t verify if that was within their acceptable limits of <40% RH. That cost them $12,000 in rework—all because of vague documentation.
Now, choosing your documentation format. I’ve worked with teams that use paper, spreadsheets, custom software, and even cloud-based tools, and each has pros and cons, but the rule is: it has to be retrievable, unalterable, and linked to the HIC’s unique ID. Paper is fine for small-scale storage, but you have to make copies (digital and physical) because paper can get lost or damaged. For large operations, digital is better. We recommend clients use either a cloud-based quality management system (QMS) or a standardized spreadsheet with conditional formatting to flag out-of-threshold readings. For example, if a HIC’s reading is above the 40% RH threshold, the spreadsheet cell turns red, so the team notices immediately. I don’t recommend handwritten notes on random sticky notes—they’re impossible to track during an audit. One of my long-time clients in the medical device space still uses paper logs, but they tape a copy of the HIC’s color chart next to each log, so any new hire can correctly match the color to the RH threshold.
A critical part of documentation is chain of custody. If the HIC moves from storage to a workbench, to a sealed package, to a testing lab, you have to track who handled it, when, and for how long. This is especially important for products that require traceability through the entire supply chain. When a HIC is placed inside a sealed component package, write that in the documentation too: “HIC SN HIC-2024-0317-0042 placed in hermetic package SN 987654 on 2024-04-12, time 15:02.” This ties the HIC’s reading directly to the final product, so if there’s a moisture-related failure later, you can pinpoint whether the issue was in storage or during assembly. Last year, we supported a client that had a military radar module fail due to internal moisture. Their documentation showed the HIC inside the module had changed to 50% RH, but they couldn’t track when that change happened because they hadn’t logged chain of custody. We helped them adjust their process, and their next audit passed with full traceability.
Common mistakes I see that ruin documentation: not noting the HIC’s calibration date, guessing the threshold instead of matching to the legend, not updating logs when a HIC is replaced, and storing documentation somewhere inaccessible. For example, if a HIC is replaced because it expired, you have to document that too. HICs have a shelf life—most are good for 12 to 24 months from manufacturing, as long as they’re stored in a desiccated environment (<10% RH). If a card is past its expiration date, its color change might be inaccurate, so you can’t use its reading. That’s another key point: note the HIC’s expiration date when you take the reading. I’ve seen teams use expired HICs, document their readings, and then wonder why their products failed—because the card had degraded and gave a false low RH reading.
Another best practice: store a copy of the HIC’s actual color (alongside the documentation) for high-stakes applications. In the past, clients would mail photos of HICs, but now we recommend using a digital log that attaches a timestamped photo of the card next to the reading. For aerospace parts, this photo is part of the audit trail. One client told me that when an auditor questioned their HIC readings, they pulled up the photo, matched the color to the legend, and resolved the question in 2 minutes—without having to dig through old boxes of paper logs. Just make sure the photo is clear, no glare, and includes the HIC’s serial number in the frame.
When readings are out of specification, documentation becomes even more important. If a HIC shows a RH higher than your acceptable limit, you have to document that immediately: who noticed it, when, what action was taken (e.g., removed the bag, replaced desiccant, moved components to a drier space), and the follow-up reading after 24 hours. For example, “HIC SN HIC-2024-0317-0047 removed from cabinet shelf 3 on 2024-04-12 at 09:15, reading shows 50% RH (threshold exceeded acceptable <30% RH). Action: replaced desiccant, sealed cabinet, retested HIC on 2024-04-13 at 10:00, reading now 25% RH. Follow-up log attached.” This creates a corrective action record, which is required by most quality standards. Skipping this step leads to non-conformities, as I saw with that semiconductor client last year.
Now, let’s talk about how to organize these records. I recommend grouping logs by storage location, batch number, or product line—whatever makes sense for your operation. For example, if you have 10 storage cabinets, name each Cabinet A, Cabinet B, etc., and each HIC in Cabinet A has a log entry linked to that cabinet’s ID. When it’s time for an audit, you can pull all logs for Cabinet A in 2024 in 30 seconds, instead of sifting through a pile of unorganized papers. For digital logs, use unique identifiers that link to your existing quality or inventory system—this eliminates duplicate entries and makes traceability seamless.
As a HIC supplier, I’ve also noticed that many clients mix up different types of HICs. Some HICs are for single use, some can be reused (though we recommend single use for most applications, as reuse can alter calibration), and non-cobalt HICs (used for medical products, since cobalt is restricted) have different color thresholds. Make sure you note the HIC type in your documentation too. For example, “Non-cobalt HIC SN HIC-NC-2024-0201-0012, 10/20/30/40 RH range, single use, reading 20% RH on 2024-04-12.” Mislabeling a non-cobalt HIC as cobalt-based can lead to incorrect documentation, especially for regulated industries.
Let’s wrap this up with a real example from a client who implemented these steps. A client that manufactures implantable medical devices was struggling with FDA audits because their HIC documentation was vague and untraceable. We worked with their quality team to build a standardized log that included: HIC serial number, calibration date, expiration date, type of HIC, location, date and time of reading, ambient conditions, photo of the HIC, and chain of custody notes. Within three months, their audit passed with zero findings. The team said the biggest improvement was that they could resolve questions in real time, instead of waiting weeks to dig through records.
If you’re still figuring out your HIC documentation process, start small. Pick one storage location, test a simple log template, and adjust as you go. Don’t wait until an audit or a failed product to fix bad documentation.
At the end of the day, documenting HIC humidity readings is about two things: protecting your products and protecting your business. Bad documentation leads to rework, audit failures, and lost revenue. Good documentation creates accountability, traceability, and peace of mind. If you’re looking to update your HIC process, or have questions about calibrated cards for your specific application, feel free to reach out to discuss your requirements.
Activated Charcoal Deodorizer References
- International Organization for Standardization. (2018). ISO 10013:2018, Quality management systems — Guidelines for documentation.
- Institute of Environmental Sciences and Technology. (2021). IEST-RP-CC003.4, Humidity and Temperature Control for Microelectronic Assemblies.
- U.S. Food and Drug Administration. (2022). Guidance for Industry: Good Manufacturing Practice Guide for Medical Devices.
- HIC Manufacturer’s Technical Manual. (2023). Humidity Indicator Card Calibration and Usage Guidelines.
Shenzhen Chunwang New Materials Co., Ltd.
Established in 1998, Shenzhen Chunwang New Materials Co., Ltd. is well-known as one of the leading manufacturers and suppliers of humidity indicator card in China. During the past two years, we have introduced advanced equipment and technology into our factory. Please be free to buy our cheap humidity indicator card made in China.
Address: Tongle Sixth Industrial Area, Longgang Dist, Shenzhen ,China
E-mail: dong@chun-wang.com
WebSite: https://www.absorbwell.com/
