Metal Bitcoin Seed Storage: Jameson Lopp’s Stress Test Results

Does Metal Bitcoin Seed Storage Work? Someone Did a Stress Test to Find Out

One of the cool things about bitcoin is that you can effectively store millions of dollars just by writing down 12 or 24 words. One of the downsides of this system, however, is securely storing those 12 or 24 words.

To solve that problem, entrepreneurs have created a metal bitcoin seed storage system. You engrave your 12 or 24 BIP38 or BIP39-encrypted passphrase onto a sheet of metal.

Infrastructure engineer Jameson Lopp recently published the results of a stress test online. Lopp, who created, works at, and founded, described the pros and cons of different metal-based seed storage systems.

In any case, Lopp’s blog post is designed to help users pick the perfect metal-based cryptocurrency storage solution.

Why Do We Need Metal Bitcoin Seed Storage?

Typically, people store their passphrase using a “paper wallet”: you write the passphrase on a piece of paper, then reference that paper whenever you need to claim your funds. Paper wallets, however, are vulnerable. A paper wallet can get ruined when wet or exposed to heat. Paper disintegrates over time.

You know what doesn’t disintegrate, melt, or get destroyed in most conditions? A piece of stainless steel. And that’s why a growing number of crypto users are using metal bitcoin seed storage solutions.

Melting Points

Steel has one of the highest melting points of all the metals. The only major metals with a higher melting point than steel’s 2500° F are wrought iron (2700° F), nickel (2646° F), and tungsten (6150° F). That makes steel an ideal type of seed storage system for protecting your key against fire.

Other crypto users have proposed aluminum, copper, and other metals, but all of these metals have relatively low melting points. Sure, they might be easier to engrave and modify, but that comes with a cost. Aluminum and copper wallets would melt in an average house fire.

Corrosion Resistance

Melting point isn’t the only consideration when choosing the perfect metal. Corrosion resistance is another factor. Events like flooding or exposure to humidity long-term could make it impossible to read your seed.

Metals have vastly different corrosion-resistance ratings, and these ratings often have little to do with melting points.

Stainless steel is one of the most popular corrosion-resistant metals. However, in the future, we might see growing availability of metallic glass or amorphous metals, which are more durable and resistant to corrosion than standard crystalline metals.

Gold, for the record, is one of the metals least likely to corrode. Other low-corrosion metals include graphite, silver, stainless steel, silver solder, and copper.

Zinc, aluminum, galvanized steel, mild steel, cast iron, and lead, meanwhile, are more likely to corrode.

Crush Resistance

Crush resistance is another consideration. Your wallet might survive a house fire. It might survive a flood. But what happens when a natural disaster causes your house to collapse on itself? That’s where crush resistance comes into play.

Crush resistance varies widely between metals. Lead, for example, is relatively soft, with a hardness rating of 5 on the Rockwell B-scale.

Cast iron (60), stainless steel-304 (88), and titanium (80) are all famously hard metals based on their Rockwell B-scale scores.

Physical Attack

You might have your seed engraved on the most durable piece of metal on the planet. However, durability means nothing if someone is able to walk up and steal that piece of metal, then capture all your funds.

How do you protect your physical passphrase against physical attack or theft?

One option proposed by Lopp is to secure your data with an additional passphrase as described in BIP38 or BIP39.

Alternatively, you can “shard” your metal backups, or split your data into a number of different parts. You put one part on a metal device in the safe in your home, for example, and another part in a safety deposit box at a bank downtown.

If you choose to shard your private key, Lopp recommends leaving some overlap:

“For redundancy you’ll want these pieces of data to overlap a bit so that losing a device won’t prevent you from recovering all of the data you need.”

Which Cold Storage Devices Underwent the Stress Test?

After detailing the pros and cons of different materials, Lopp lists some of the top cold storage solutions available today. Lopp purchased each of these wallets before subjecting each to a stress test.


Billfodl is a stainless steel device that comes with prefabricated letters. The device claims to be waterproof, fireproof, shock-proof, hackerproof, and even “you-proof” (the device makes it difficult to mishandle your seed phrase or have it inadvertently destroyed by loved ones).


Cryptosteel is another stainless steel device with prefabricated letters. The device claims to be fireproof up to 2200° F – which is almost as fireproof as top stainless steel allows (with melting proofs of up to 2500° F). Overall, the design is similar to Billfodl.

Crypto Key Stack

Crypto Key Stack uses black anodized stainless steel plates to protect your passphrase from fire up to 2200° F, which is twice the average temperature of a house fire. The device also claims to be waterproof and rustproof. Unlike the Cryptosteel and Billfodl, it doesn’t come with its own stainless steel letters. Instead, it comes with an engraving tool and you etch the names on yourself.


ColdTi claims to be fireproof, waterproof, timeproof, and tamper-resistant with a very high melting point and extreme durability.


Bitkee advertises a 3000° F melting point along with corrosion resistance thanks to its use of grade 2 Titanium with a rating of ASTM B265, Rockwell B 65, 40K psi. The manufacturer describes Bitkee as durable, fireproof, waterproof corrosion resistant, and invulnerable to software and hardware crashes.

Other Cold Storage Devices

Lopp tested all of the devices above. However, he also mentioned a number of other devices that he didn’t end up testing, including:

  • Bitcoin Firesafe
  • CryptoHex
  • Cryo Card
  • Blockplate
  • SeedSteel
  • The Hodl Wallet

Lopp wanted to test all of these solutions, but they were out of stock or redundant.

What Happened During the Stress Test?

Lopp tested each of the cold storage solutions above. He engraved or added words to each wallet, then subjected each wallet to extreme conditions. Here’s what happened.


Lopp described Billfodl as easy to setup. All you need is a flathead screwdriver to unlock it. Then, start sliding in the laser-engraved stainless steel letters.

“It took me a few minutes to figure out how to actually unlock the gate in order to slide in the letters since there were no instructions provided,” explains Lopp.


Cryptosteel’s setup was nearly identical to Billfodl’s setup. You use a flathead screwdriver to unlock and slide-in pre-stamped metal pieces. The letters are stamped on each side.

Crypto Key Stack

Crypto Key Stack lets you engrave or stamp your seeds onto stainless steel cards. Lopp described the engraving process as “easy, although the granularity of the engraver leaves a bit to be desired.” It would be easy to screw up a letter in a way that makes it ambiguous to read – like writing a B instead of an 8 or a 1 versus an l. Alternatively, you can get a stamping kit and use a hammer or mallet.


“I felt like the space was cramped,” Lopp said of ColdTi’s seed storage system. He also found that reading the letters was more difficult on ColdTi because there was limited contrast against the background.


Bitkee is a unique solution because it comes with the keys already laser-engraved on the metal. The key and QR code are neatly printed.

Stress Test #1: Heat

Lopp subjected each seed storage system to heat. He purchased a butane torch on Amazon capable of achieving 2500° F. Then, he subjected each cold storage solution to 20 minutes of heat. How did each seed storage system fare?


Billfodl’s tray experienced “catastrophic failure” when exposed to the heat of the blowtorch. Billfodl’s tray warped, causing a number of letters to fall out. The device itself remained intact, but the passphrase was destroyed.


When exposed to heat, Cryptosteel “held up quite well and almost all the letters stayed in their slots,” reported Lopp. However, some letters did fall out, making the passphrase unintelligible. Lopp considered Cryptosteel’s stress test “a catastrophic failure due to data loss.”


ColdTi also experienced a catastrophic failure – but only when engraving it instead of stamping. The engraved words were “completely lost” at the point of heat application, although the stamped words were still visible. If you use ColdTi and want maximum protection, then you’ll want to stamp it. ColdTi’s screw also failed under heat.

Crypto Key Stack

The screw near the heat deformed slightly on the Crypto Key Stack cold storage solution. However, the screw still worked, and Crypto Key Stack survived the heat test.


Lopp reports that Bitkee “held up to heat extremely well”, with the only noticeable difference being “additional coloration on the metal.”

Stress Test #2: Corrosion

The second stress test measured corrosion. Typically, corrosion occurs over many months or years. The Statue of Liberty, as you may know, was not originally green. To replicate long-term corrosion, Lopp scraped all of the wallets with sandpaper to remove any protective coating. Then, he dumped each wallet into a bucket of muriatic acid for 30 minutes.

Lopp also added pre-1982 pennies because copper purportedly accelerates the corrosion process. After being dumped in the acid bath, a bunch of bubbling started to take place.

The bubbling was the screws that were holding the ColdTi together. They completely dissolved in the acid bath.

Lopp then pulled out the wallets, washed and dried them, and coated them with a spray of salt and hydrogen peroxide for additional oxidation. “This resulted in some rust forming but it wasn’t nearly as impressive as the results from the acid.”

Stress Test #3: Crushing

Finally, Lopp found someone with access to the Duke Physics department’s machine shop, where they have a hydraulic press capable of creating 20 tons of force.

“Unsurprisingly it turns out that none of these devices are so strong that they can withstand 20 tons of force without deforming. But for the purpose of these tests we’re not interested in the deformation so much as whether or not it leads to data loss.”

Billfodl and Cryptosteel

Both Billfodl and Cryptosteel were the more crush-resistant wallets of the bunch. However, the rail-style design means that any deformation causes numbers to slide out, making it impossible to decipher the seed.

Crypto Key Stack

After the crush test, Crypto Key Stack was visibly warped and deformed, but the letters were all still readable and correct.


ColdTi was deformed, but it did not result in any additional data loss compared to the original failure during the heat stress test.


Bitkee was also deformed but did not lose any data readability.

The Final Results

Lopp tallied each device’s ratings based on their performance during the stress test. Here’s how each device fared:

Billfodl: C Overall (C Heat, A Corrosion, D Crush)

Bitkee: A Overall (A Heat, A Corrosion, A Crush)

ColdTi: C Overall (D Heat, C Corrosion, A Crush)

Crypto Key Stack: A Overall (A Heat, A Corrosion, A Crush)

CryptoSteel: B Overall (B Heat, A Corrosion, D Crush)

Overall, none of the storage solutions were perfect based on Lopp’s stress testing. However, he also subjected each wallet to extreme conditions beyond what any ordinary wallet could be expected to withstand.

So which cold storage solution does Lopp use? He doesn’t use one!

“I’ve never actually used physical devices like this for my own needs. My personal solution is fully digitized because I can achieve the highest level of security and redundancy with cryptographic tools. The downside is that it takes a lot of technical sophistication and effort to achieve.”

Lopp’s full stress test post is worth a read here.

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