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Tawnos's Toolbox: Foil Curling

Over the past few years, I've read an increasing number of complaints about foils curling as well as claims that card quality has decreased substantially in the past few years. Despite documented evidence backing the complaints that some sets' foils curl, my cards have remained flat for even the most criticized of recent sets. In particular, complaints about Commander Legends made me take notice because I'd opened a box in the hopes of playing some games for an event, but I was too late in signing up and just left my cards sitting on the playmat for at least a month. Yet, despite the complaints of excessive curling, my foils were quite flat:

Foil Card Construction and Curling Causes

Foil cards consist of three layers: metal foil with the face printed on it, glue, and a cardboard back. If you've spent any time looking into the causes of foil curling, you've inevitably come across comments or articles about how curling is related to changing humidity in the cards. That theory is correct—humidity changes cause expansion and contraction of the fibers that make up the cardboard side of the card, causing it to swell or shrink based on how much moisture is added or removed. The foil layer is glued to one side of the printed cardboard back half at some level of humidity. When the fibers swell or shrink, the foil does not, causing conditions I'll describe as "arching" (curling with the foil on the convex side) and "cupping" (curling with the foil on the concave side).

Unfortunately, far too many of those articles suggest using desiccant to "keep the cards dry and prevent curling." It's a noble attempt to solve the curling issue, but it brings an underlying assumption that the default state of the cardboard side of foiled cards is "dry." In reality, it seems the average moisture level of the cardboard is around 60–65% when printed. Putting a foil card into desiccant removes moisture from the cardboard half, shrinking it and causing the card to arch. In only 12 hours, half of the above cards were dried and made fully arched by the desiccant:

To verify that humidity could also be used to "repair" these cards, I took half of the arched cards, put them in a 100% humidity environment, and checked their status every 12 hours. Ultimately, it took 48 hours for the cards to hydrate to slightly higher humidity than they started. This resulted in cards that were now minorly cupped. The other half were left in the air of the basement and got noticeably flatter but were still arched beyond playability.

This taught me two things:

  1. It's much quicker to dry out a card than to rehydrate one.
  2. My basement's humidity is close to ideal for storing the cards.

I live a short drive east from Seattle; my basement stays at around 65% relative humidity year-round. Here, the colder months are also the most humid months, offsetting the dehydration that forced-air heating causes. During the summer, the outside humidity drops as the temperature warms, but seldom to the point where we need significant air conditioning. This is an important consideration depending on where you live. In climates where the colder months are also dry, especially those that get below freezing, forced-air heating can reduce indoor humidity to below 30%. This is drastically below the humidity that any foil appears to have been printed and will quickly arch your cards. In areas with high humidity that don't require air conditioning or heating, cards may be prone to cupping as they absorb excess moisture.

Testing a Solution

While waiting for my arches to rehydrate, I dug through some of my collection and found an assortment of foils from various sets. They, too, have remained flat despite being stored in a bulk box in my basement. Armed with this mix of historical foils, the Commander Legends cards that inspired this investigation, an estimate for the target humidity, and an excess of time on my hand, I purchased three packs of humidity regulators from Amazon. These packs are cheap—less than a dollar each—and typically are used with high-quality cigars or cannabis to maintain an ideal level of humidity for a year or two of storage. I divided all of the foils among the humidity control packs and put them in some cheap deck boxes I had lying around.


After one week, each set of cards had minor changes. Cards at 55% humidity dried out slightly, causing minor arching in the previously flat foils and not affecting the previously dehydrated arches.

Cards at 62% remained mostly flat, with the dehydrated arches and the overhydrated cups flattening slightly, indicating that both were moving closer toward their ideal humidity.

Cards at 72% all showed minor cupping, with the exception of the arched cards that were not forcibly rehydrated—they were still slightly arched.

Moisture-Loss Prevention for Play and Storage

During this testing, I began wondering about how well sleeves protect against curling and how long that protection lasts. To test this, I grabbed three matching Eclipse Matte sleeves, a KMC Perfect Fit inner, and a KMC Perfect Hard inner to sleeve up three of the flattest Commander Legends foils from my ongoing experiments. All three of these cards were placed back into the sealed bucket of desiccant and checked every 12 hours.

After 48 hours, it was clear that single sleeving only provided minimal protection from cards drying out and curling. However, there didn't appear to be any change in the double-sleeved cards, regardless of which inner sleeve was used. At this point, I took the single-sleeved card out of testing and put it into the 72% box to rehydrate it.

The remaining two cards I left in the bucket of silica gel, checking every few days until I saw a level of curling consistent with the single-sleeved card. After two weeks, both double-sleeved cards were curved slightly from moisture slowly making its way past the sleeves, and no difference could be seen between how much moisture escaped from the Perfect Fit versus the Perfect Hard.

Longer-Term Results

Just over a month after starting the experiment, the cards were stable enough that I felt safe concluding the part of the experiment that went into this article. The results surprised but excited me because they showed a clear distinction between Commander Legends cards and other cards in my collection.

Cards at 55% had the least amount of change. Older foils stayed relatively flat or slightly arched. Cards from Commander Legends didn't seem to get noticeably better or worse.

Cards at 62% provided the greatest surprise to me. There was a clear distinction between most of the older cards and the Commander Legends prints. Every older card had cupped very slightly, while the Commander Legends and Time Spiral Remastered foils became mildly arched. The cards in the center of the picture were the ones that were dehydrated and arched initially—they had not yet rehydrated to flat but were quite close

Cards at 72% were all some degree of cupped (almost the same, in fact), with the exception of the two cards I was rehydrating from the double-sleeved experiment. I only removed their outer sleeves, but they still had flattened significantly since I put them in the box two weeks before.

Conclusions, Recommendations, and Theories for Future Research

After the above photographs were taken, I took all of the cards from the experiment and put them in the 72% box. My theory was that this would cause minor cupping on all of the cards as they would overhydrate slightly. So far, it's been working pretty well, but it seems that the cards I forcibly dehydrated without putting into 100% humidity environment will take even longer to stop arching.

Based on what I've seen, getting and keeping foils flat enough for tournament play are possible, and it's easy (but time-consuming) to fix even badly curled foils. The first thing to do is identify what kind of curling you see. Second, store unsleeved curled foils with either the 55% or 72% humidity control pack until they look flat enough to play with. Third, double-sleeve them, then store them with a 62% pack in a box that does not get a lot of circulation (it doesn't need to be airtight, but that helps). It would not surprise me to see a custom deckbox builder incorporate a space for humidity control into the boxes, which would make it much easier to slip one of these control packs in. Based on some other tests I didn't photograph, it may work faster if the packs are along an edge of the card, but the difference in my tests was minor, at best.

The one-month results of 62% surprised me because they clearly showed a difference between the Commander Legends and older cards I pulled. However, I'm wondering if there's a correlation between when or where special sets, such as Commander Legends, are printed that leads to higher complaints of foil curl, especially during the winter, when half the northern hemisphere is using some form of dehydrating form of heating. The difference in curling direction showed that humidity was likely higher in the paper used for Commander Legends than that in many other prints, and my limited amount of Time Spiral Remastered foils indicates slightly lower humidity cardboard that is still higher than the average set. If I get a chance and find the desire, I'll dig through more cards to get a broader look into the timeline of set releases and see if I can find a pattern. Until then, I hope this helps you!

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